Business products:


for conical taper joints (laboratory glassware).

PTFE (polytetrafluorethylene) is chemically equivalent to Teflon
® PTFE from DuPont.
Home (English) Business products: Glindemann PTFE Sealing Rings Research publications of  Dietmar Glindemann
News Contact Impressum
English   Deutsch Francaise  Español  Japanese日本語      Chinese

1 sales unit = 1 pack of 50 PTFE sealing rings on an adapter tube (polypropylene) fitting the diameter of the glass joint.
Kartusche Farbphoto mit Glas und Ring und Pfeil.jpg (12270 bytes)


Good news: We have our product permanently in stock for delivery to our distributors. In case your local distributor says that the product is currently not available, you may buy from another distributor listed in our table below.

Please contact Dr. Glindemann at if you currently experience ordering problems with your distributor.

Worldwide customers: "GLINDEMANN PTFE Sealing Rings" are sold by Sigma-Aldrich (Millipore Sigma). Search Sigma-Aldrich web-shop for "glindemann" or enter Sigma-Aldrich catalogue number from the table below. You may also search Google for a Sigma-Alrich catalogue number, such as Z502081, and will find a variety distributors who sell the product.

USA customers: does export worldwide including the USA (most  other European based distributors do not export to the USA). If you are based in the USA and can not open an account with Sigma-Aldrich (Millipore Sigma) you can order from

Prices of GLINDEMANN PTFE Sealing Rings
Our recommended list prices for end-users for the most common sizes (for joint 14 to joint 29)  are around 30 € per sales unit (1 sales unit = 1 pack of 50 PTFE  rings).
In practice, end-user prices for the most common sizes (for joint 14 to joint 29)  range from 20 € to 60 € per sales unit (1 sales unit = 1 pack of 50 PTFE  rings) dependent on distributor and order quantity. Most distributors offer discounts on bulk quantity orders.

GLINDEMANN®-PTFE sealing rings   
for ground taper (conical) joints

Literature Download
Download Technical Publication 1
(published in journal Fusion of the American Scientific Glassblowers Society ASGS).

Download Technical Publication 2
(Flyer with Tips and Tricks)
Goettinger Bogen 15
D-06126 Halle
ph:  0345  6879948 (country code 49)
(from the USA/Canada: dial 011 49 345 6879948, else dial 00 49...)
fx:   0345  6871333   (country code 49)
Internet :   

Links in this site:
Distributors and catalogue numbers of Glindemann Sealing Rings
Glindemann rings - what exactly is for sale?
Application: For what are
Glindemann Sealing Rings good for?
Procedure: Instruction on how to apply Glindemann Sealing Rings
Frequently asked questions and Know How on Glindemann Sealing Rings
Test reports on Glindemann Sealing rings (references)
Links on laboratory glass ware in the internet and to


List of distributors of GLINDEMANN® sealing rings and their catalogue numbers
(to find distributor addresses in single countries, see next table)
Joint size
(nominal maximum diameter, mm)
7 10 12 14 19 24 29 34 45 70 Distribution in
Joint size (actual maximum diameter / mm) 7,5 10 12,5 14,5 18,8 24 29,2 34,5 45 71  
Joint diameter - Do not be confused by joint names such as  "14,5" instead of "14",  "18,8" instead of "19", or  "29,2" instead of "29". Glindemann sealing rings fit these joints.
Joint length - Do not be confused by joint names such as joint 29/32 which means for this joint 29 the length is 32 mm. Glindemann sealing rings fit joints of all lengths, preferably medium-length joint and long-length joint. With short-length joint you may have to inflate the diameter of a sealing ring by stretching with little force.
Glindemann Catalogue No.  K7 K10 K12 K14 K19 K24 K29 K34 K45 K70 Distribution in
Number of Sealing rings /  unit  (pck) 50 50 50 50 50 50 50 50 50 50  
Distribution worldwide (200 countries) by SIGMA-ALDRICH  (named Millipore Sigma in USA/Canada).
Search the Sigma-Aldrich shop for "glindemann" or enter Sigma-Aldrich catalogue number below.
Buy with the Sigma-Aldrich product number from your local distributor:
In North-America (USA, Canada, Mexico), you can also order from Fisher Scientific, Thomas Scientific, Krackeler Scientific, etc., using the Aldrich-catalogue numbers. Please contact Dr. Glindemann at if you currently experience ordering problems.
Sigma-Aldrich Labware Catalogue)   Z501980   Z502081 Z502200 Z502316 Z502413   Z502529   Worldwide 200 countries
Other worldwide or regional distributors.
USA customers:
If you wish an alternative to Sigma-Aldrich you can order from (search for 'glindemann' or click Home > Laboratory > Distillation, Separation, Filtration > Distillation, Synthesis > NS Joint Accessories > PTFE sealing rings for jointed glassware. Most other European based distributors do not export specifically to the USA.
Joint size maximum diameter / mm 7 10 12 14 19 24 29 34 45 70 Distribution in
Lab Unlimited Carl Stuart Group (Lab Unlimited is a partner of 4AJ-9011663 4AJ-7622596


4AJ-9011665 4AJ-9011666 4AJ-9011667



Worldwide, incl. North-America USA
Lab Logistics Group (LLG), A network of national partners who distribute in many countries   9011663 7622596


9011665 9011666 9011667



  Europe, Australia, Israel, Japan, New Zealand (worldwide)
Carl Roth GmbH,
with partners for
    T221.1 E699.1 E700.1 E701.1 E702.1   T222.1   Europe (worldwide, except USA)
AJ Cope & Son Ltd,
      QZZ27/14 QZZ27/19 QZZ27/24 QZZ27/29 QZZ27/34 QZZ27/45   UK, Ireland
in Germany

(respectively local country branches)
  Germany, EU, Switzerland, UK
VWR International
in Germany

(respectively local country branches)
2016251 2016252 2016253 2016256 2016258 2016260 2016262 2016263 2016264 2016266 Germany, Austria, Switz., Poland, Russia, UK, Italy
is an e-marketplace used by distributors LLG and Carl Roth.  Search their catalogue numbers or 'glindemann'
(including France, Italy, Netherlands, Spain, UK)
LR. Vetter Laborbedarf
Selling at competitive prices at small order quantities as
low as 1 unit of 50 rings.
DKA-7 DKA-10 DKA-12 DKA-14 DKA-19 DKA-24 DKA-29 DKA-34 DKA-45 DKA-70 Germany, Europe
AMSI-Glas AG 6.300.007 6.300.010 6.300.012 06.300.014 06.300.019 06.300.024 06.300.029 6.300.0344 6.300.045 6.300.070 Switzerland

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Addresses of distributors worldwide
(examples, can be subject to change over time)
(to find catalogue numbers, see table above)
Catalogues of company (click on links to see addresses)


Phone, Fax, e-mail Catalogue numbers
(see table above)
Country of Distribution
Sigma-Aldrich (Sigma-Aldrich Labware Catalogue)
Search for "glindemann". See "worldwide offices" in 200 countries.
ALDRICH Worldwide,
200 countries
Lab Logistics Group (LLG). LLG is the central organisation of a cooperative of about 30 privately owned laboratory dealers in Europe, Asia and Australia.
In case you do not find the product in the web-shop of your dealer, contact them with the LLG catalogue number and they will order the product from LLG for you. This network of national partners distributes in many countries.
Lab Logistics Group (LLG) National LLG partners in many countries
Lab Logistics Group LLG  (logistics centre in Germany)

Postfach 1416
D-37004 Göttingen, Germany

Fx ++49(0)2225-948691

Lab Logistics Group (LLG)  
Lab Logistics Group LLG in Austria:

Bartelt GmbH

Bartelt GmbH
Neufeldweg 42
AT-8010 Graz

Fon: +43 (0)316/47 53 28-0
Fax: +43 (0)316/47 53 28-55
Lab Logistics Group (LLG) Austria
Lab Logistics Group LLG in UK & Ireland:

Lab Unlimited Carl Stuart Group

Lab Unlimited - Carl Stuart Group, Quadro House
Frimley Road
Camberley, Surrey
GU16 7ER
United Kingdom

Fon: +44 (0)8452/30 40 30
Fax: +44 (0)8452/30 50 30
Lab Logistics Group (LLG) UK, Ireland
(+ worldwide order mailing)

Lab Logistics Group LLG in Finland:

Labnet Oy

Labnet Oy
Mäkituvantie 7
FI-01510 Vantaa, FINLAND
Fon: +358 20 7413 170
Lab Logistics Group (LLG) Finland
Lab Logistics Group LLG in France:

Sodipro S.A.

42, rue Ambroise Croizat, BP 307, F-38434 Echirolles Cedex, France

Ph: 0033 (0)4 7623 3927, Fx 0033 (0)4 7623 2412,
Lab Logistics Group (LLG) France
Lab Logistics Group LLG in Denmark:

Buch & Holm A/S

Buch & Holm A/S

Marielundvej 39
DK-2730 Herlev

Fon: +45 (0)44/54 00 00
Fax: +45 (0)44/92 31 00
Lab Logistics Group (LLG) Denmark
Lab Logistics Group LLG in Sweden

Buch & Holm

Buch & Holm

Box 10058
SE-200 43 Malmö

Fon: +46 (0)40-30 50 30
Fax: +46 (0)40-30 50 39
Lab Logistics Group (LLG) Sweden
AJ Cope & Son Ltd,
on-line shop
The Oval, Hackney Road, London E2 9DU, UK
Ph: (0044) 0207 729 2405, Fx: (0044) 0207 729 2657,
Lab Logistics Group (LLG) UK, Ireland
Lab Logistics Group LLG in Isreal

BDL - Beith Dekel
BDL - Beith Dekel
Etgarim Building, 16 Hatidhar Street P.O.Box 2094 IL-43665 Raíanana
 Fon: +972 (0)9/76 11 800 Fax: +972 (0)9/74 20 073 Lab Logistics Group (LLG) Israel
Lab Logistics Group LLG in Russia

WENK LabTec Russia
WENK LabTec Russia ul. Derbenevskaya 20, bld. 18, office 2 115114 Moscow  Tel.: +7 (425) 662-12-34 Lab Logistics Group (LLG) Russia
Lab Logistics Group LLG in Spain

Serviquimia, S.L.
Serviquimia, S.L.

Pol. Ind. de Constantí
C/Dinamarca, s/n
ES-43120 – Constantí (Tarragona)

Fon: +34 (0) 902 201 002
Fax: +34 (0) 977 524 478

Lab Logistics Group (LLG) Spain - Espagna -
continue and find a complete list of national partners of LLG around the world    
Catalogues of company (click on links to see addresses)


Phone, Fax, e-mail Catalogue numbers
(see table above)
Country of Distribution
Carl Roth GmbH (Roth) is a Germany based independent laboratory provider with 5 offices in 5 Countries, and with a network of a list of partners for 100 countrie on all continents. You can contact your local Carl Roth partner or otherwise contact directly from a list of export service specialists of Carl Roth.
Customers in USA and Canada: contact Brunschwig Chemie B.V., Postbus 74213, NL 1070 BE Amsterdam, Phone: +31 20 611 31 33, Fax: +31 20 613 75 96,,
Carl Roth GmbH, Germany

Schoemperlenstr. 3, D-76185 Karlsruhe, Germany

Ph++49 (0)721/5606-0,
Fx++49 (0)721/5606149

Carl Roth (Roht) list of partners for 100 countries
Brunschwig Chemie B.V. Brunschwig Chemie B.V., Postbus 74213, NL 1070 BE Amsterdam Phone: +31 20 611 31 33, Fax: +31 20 613 75 96, Carl Roth (Roht) USA, Canada
Carl Roth in France

ROTH Sochiel E.U.R.L.

3, rue de la Chapelle/B.P. 11, F-67630 Lauterbourg, France

Ph: 03 88 94 82 42
Fx: 03 88 54 63 93,
Carl Roth (Roht) France
Carl Roth in UK

Techmate Ltd.
(Rotec Scientific)
Techmate Ltd
10 Bridgeturn Avenue,
Old Wolverton, Milton Keynes,
MK12 5QL, UK

Ph +44 (0) 1908 322 222

Carl Roth (Roht) UK, Ireland

Carl Roth in Ireland

Astech Ireland Ltd.

Unit 47, Southern Cross Business Park, Bray
Co.Wicklow, A98 H6D6, Ireland
Carl Roth (Roht) Ireland

Carl Roth in Austria

LACTAN® Vertriebs.-ges. m.b.H. & Co. KG

Vertriebsgesellschaft m.b.H & Co KG
Puchstrasse 85
A-8020 Graz
Ph: 0316/323692-0
Carl Roth (Roht) Austria
Carl Roth in Poland

Linegal Chemicals Sp.z o.o.
Linegal Chemicals Sp. z o.o.
ul. Kasprzaka 44/52, PL-01-224 Warszawa
Ph: 022/632-32 21 w.-33 74,-31 92,-32 91,
Fx: 022/631-72 81
Carl Roth (Roht) Poland - Polska
Carl Roth in Spain

C/Balmes, 245 6ª planta
08006 - Barcelona - España
Tel +34 932 380 094
Fax +34 932 181 773
Carl Roth (Roht) Spain - Espagna
Carl Roth in Czechia - Ceska


P-LAB a.s.
U Pekáren 1
102 00  Praha 15-Hostivař

Ph: +420 271 730 800
Carl Roth (Roht) Czechia - Ceska
Carl Roth in Norway

Chiron AS
Chiron AS, Stiklestadveien 1, NO-7041 Trondheim, Norway T: +47 73 87 44 90
F: +47 73 87 44 99 E:
Carl Roth (Roht) Norway
Carl Roth in China

continue and find a complete list of national partners of Carl Roth around the world    
Fisher Scientific Germany
(respectively local country branches)

Im Heiligen Feld 17 58239 Schwerte

Ph++49 (0)2304 / 932-800
Fx++49(0)2304 / 932-957

Fisher Scientific Germany Germany, EU, Switzerland, UK
VWR in Germany
(respectively local country branches)

John Deere Str. 5,
D-76646 Bruchsal, Germany

Ph++49 (0)7251/717-0
Fx++49 (0)7251/717-182

VWR (ealier Merck Eurolab) Germany, Austria, Switz., Poland, Russia, UK, Italy
LR. Vetter Laborbedarf e.K. Herrenberger Str. 5, D-72119 Ammerbuch, Germany Ph++49(0)7073/6936,
Vetter Germany, Europe

Geismet 11, CH-4317 Wegenstetten AG, Switzerland

Ph ++41-(0)61-8739093,
Fx ++41-(0)61-8739094
AMSI-Glas AG Switzerland



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Glindemann rings - what exactly is for sale?
Available for standard taper joint sizes from 7 to 70 mm diameter.

1 sales unit = 1 pack of 50 PTFE sealing rings on an adapter tube (polypropylene) fitting the diameter of the glass joint. Packed in a labeled Zip-bag including information in several languages.

Kartusche Farbphoto mit Glas und Ring und Pfeil.jpg (12270 bytes)


Foto: For sale is 1 pack of 50 PTFE sealing rings on an adapter tube (polypropylene) fitting the diameter of glass joint 29 mm, Glindemann-product-no. K29.


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Instruction where to use and how to use GLINDEMANN®-sealing rings
Application: Laboratory work with glass equipment and chemical storage containers often demands hermetic and clean sealing of conical joints and stoppers. Joint grease is often not optimal (dissolution, contamination, leaking). The known PTFE-joint sleeves and stoppers are expensive and not very tight. Therefore, a fine PTFE-ring seal made off PTFE (known as Teflon) on ground tapered glass joints has been developed.
Use for hermetic sealing of equipment and containers without grease. Pressure- and high-vacuum tight (gas leak rate below 10-6 mBar l /sec). Chemically resistant and tight (solvent leak rate below 0.2 mg/day). Temperature resistant (-200 to +300oC). No irreversible jamming of the joint. Useable with all joint clamps. Reusable. Available for all joint calibres: NS 7, 10, 12, 14, 19, 24, 29, 34, 45, 50, 60, 70.

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Slip a sealing ring onto the male part of the joint.
The ring adheres by elastic tension. One ring is normally enough. Two rings with about 3 mm distance. Make sure that the ring is not twisted.

For sale: 50 sealing rings on a tube, fitting the diameter of the male joint part.
Be aware that for the application on rarely used short-length joints the adapter opening can be increased in diameter to fit the joint.


The sealing ring looks on good  joints "tightly" transparent like grease.

Gently press the glass parts together. The ring must look transparently "tight" all around. Do not break the joint by overstressing. For less smooth glass joints a miniscale amount of grease, solvent or water should be added to the ring as softener. The glass parts of the joint can also be rotated and rubbed to produce microscopic PTFE-filings which smooth the glass.

The sealing ring becoming "visibly" tight
On the left: Ring before pressing the 2 joint parts together

Centre: Ring after pressing - transparently like grease. Under pressure the PTFE, although free of grease, flows like grease into the uneven surface of the ground joint

On the right: Compared to a greased joint, equally transparent. But grease is not solvent resistant and not very clean.

Disconnect the joint by moving one part of the joint back and forth (do not pull). With 2 rings extra motion back and forth.

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Frequently asked questions and Know How on PTFE sealing rings for Taper Joints

QUESTION: Ordering. Where can I order these PTFE sealing rings? ANSWER: Search the list of distributors at this homepage. If your home distributor is not on the list ask it to manage to buy sealing rings from one of the listed distributors for you.

QUESTION: Sizes. Are sealing rings available for all joint sizes? ANSWER: Yes. Rings are available for 7...70 mm taper diameter.

QUESTION: How does the PTFE ring seal work?
ANSWER: The plastic PTFE (known as Teflon) of the sealing ring acts similar to joint grease. But PTFE is much more clean and chemicly inert than joint grease. The PTFE flows under  high pressure slowly like grease or wax into the uneven spots of the ground glass surface. By this cold flow the free leakage volume between the 2 joint parts is filled and sealed by PTFE. PTFE is in fact much harder than grease or wax. To make PTFE flowing like grease it must be under a very high pressure. This pressure is produced by pressing the 2 glass joint parts together. But the force to produce this pressure is applied to the PTFE and the glass as well. This force can break the female part of the glass joint by tensile stress. But the glass is of course not allowed to break ever. Therefore, the PTFE ring is shaped to contact the surface of the ground joint only at a very small area (just the area of the 0,6 mm wide ring). If you force the 2 glass joint part together they contact each other only via the small PTFE ring. This relatively small force results therefore in a comparatively large deformation pressure on the PTFE. With this theory on PTFE ring seals in mind you can use the following rules to use these rings more efficient: Any factor which makes the PTFE more soft makes the seal better (high temperature, presence of traces of plasticizers, solvents, water, grease). Any factor which makes the ground glass surface more smooth makes the seal better (polishing of the glass surface). Any factors which gives the PTFE more time to flow makes the seal better (usually the final sealing is better a few hours after pressing the joint together).

QUESTION: Joint Clips. Can I use these PTFE sealing rings with common joint clips? I tried Keck®-type clips with joint sleeves (PTFE) with sealing ribs and the clip did not fit.
ANSWER: Glindemann rings are very thin (0,07...0,1 mm) and can therefore normally be combined with all types of joint clips (clamps), including Keck-type clips made of plastic or nickel metal or PTFE-coated metal. In addition, all types of adaptable joint clips with springs and screws can be used.

  Foto: Glindemann ring combined with Keck® joint clip   Foto: Glindemann ring combined with Clipox® joint clip

QUESTION: I have doubts that a PTFE ring can seal a glass joint properly. I used PTFE-sleeves and found they have no sealing properties compared to a bare glass joint.
ANSWER: The common PTFE sleeves which do not have sealing ribs have in fact no sealing effect because they do not work like PTFE rings. PTFE sleeves that contact the whole joint do not allow a sealing pressure high enough to make the PTFE flowing like grease. PTFE sleeves seal much better if they have sealing ribs (groove, profile) but the are still not useful for a long static vacuum.

QUESTION: Sealing Containers. Can I use the PTFE sealing rings to seal containers with glass taper stoppers? (Reagent tubes, flasks, erlenmeyer flasks, bottles)
ANSWER: Definitely, this works great. You fill find, that the PTFE sealing ring will make the glass stopper fixed in the container. Therefore, a slight overpressure in the bottle will not push out the glass stopper. To loosen the glass stopper, do not pull the joint parts apart because this needs too much strength. Instead, move the stopper to and from several times or rotate one joint part.

QUESTION: I can not remove the stopper with a sealing ring from the joint or bottle. Why are the glass joint parts with a sealing ring stuck if I try to pull them apart?
ANSWER: Do not pull the joint parts apart because this needs too much strength. Instead, move the stopper to and from several times or rotate one joint part.

QUESTION: Can I use the ring more than one time?
ANSWER: Yes. The ring can be removed from one joint and can be transfered to another joint. But scratches and dirt can make it less tight over the time.

QUESTION: How can I remove the PTFE sealing ring from the glass joint?
ANSWER: Just slip it off. The PTFE rings adheres to the male glass joint just by elastic tension, which prevents the PTFE ring from falling of the male glass joint.

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QUESTION: Extra tight seal. I used a PTFE ring seal and found the sealing not proper enough.
Inspect the seal if it looks transparently "tight" all around the joint. If there are "bad" looking spots (one millimeter is enough to cause leakage) then the ring is probably scratched or dented.
Some times the surface of the ground joint is simply to rough to fit the PTFE ring seal.
There are different possibilities to smooth out the roughness of ground jointed glass ware.
The joint with a PTFE ring seal can be rotated and rubbed to produce microscopic PTFE-particles which smooth the glass at the PTFE-contact zone forever. This zone of the joint looks like greased but it is in fact a layer of small PTFE particles which fill out the uneveness of the ground glass. To make the smooth contact zone broader move the PTFE ring on the joint and rotate the joint parts again. Remove larger visible PTFE-fibres after this procedure. The PTFE-ring used for rubbing has to be sacrificed often because it looses larger PTFE-particles which make the ring uneven.

wpe5.jpg (14027 bytes)Foto:
Extra tight seal.
Smooth a 2 mm zone of the male glass joint with PTFE filings from a ring by rubbing. Sacrifice this ring used for rubbing. Slip a new PTFE Ring onto the smoothed zone. This extra smoothing will result in an almost hermetic extra tight seal.
But you can of course use PTFE sealing rings without this procedure, for most purposes.

Another possibility is to soften the PTFE sealing ring.  This can be performed by applying a micro scale amount of grease or solvent or water.Do not clean your jointed glass in Potassium Hydroxide solution which makes ground glass even more rough. You can also ask your glass blower for slightly polishing the joints. A simple home made fire polishing procedure is to direct a very hot welding flame (more than 2000oC) for a few seconds (do not deform the joint) directly around the grounded glass surface.
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QUESTION: Extra clean work: How can I extra clean the PTFE ring for ultra clean work (biochemical, pharmaceutical, analytical, organometal work) ?
ANSWER: You can either bake the ring or you can extract contamination with solvents.
Baking: The PTFE ring can be baked at 300 oC in an oven. But do NOT put the plastic storage tube at heat over 100 oC! Slip the PTFE ring on a male glass taper stopper to prevent it from shrinking .
Solvent extraction: You can bathe, purge or rinse the PTFE rings with any useful solvent (PTFE takes any organic solvent). You can also put many PTFE sealing rings alltogether in a Soxhlet Extractor and rinse them with the solvent, which has a boiling temperature below 70 oC (at higher temperature, the rings will start to shrink).
Take care, that this cleaning (baking or solvent rinsing) will make the PTFE less soft and reduce the sealing power slightly. If you want to soften the PTFE ring again, you can add a micro amount of any greasy, oily or slippery chemical  which does not harm your laboratory work.

QUESTION: How can I prevent that the sealing ring teared up and fell off the joint after baking/heating over 200 oC?
ANSWER: Slip the ring before heating on the thinner part of the taper joint.

QUESTION: I took the ring off the joint and it contracted to be too small to install it again on a taper joint.
ANSWER: You can inflate the ring to fit again the joint. Inflate the ring with the plastic adapter which you bought together with the rings from your trader. You can also use two fingers, sticks, nails etc.
wpe6.jpg (8779 bytes)Foto:

Sealing ring contracts (shrinks)
if removed from the joint.


wpe3.jpg (12584 bytes)

QUESTION: The sealing ring became to large in diameter and fell off the joint.
ANSWER: The diameter of the ring can be decreased by use of high temperature of 100...300 oC (oven, lighter, Bunsen burner).


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Chemists' user opinions, test reports and literature about GLINDEMANN rings

1. Test report of GLINDEMANN-PTFE-sealing rings for ground tapered joints
from: Dr. Andreas Bolte, Group Prof. Dr. Borislav Bogdanivic, Max-Planck-Institute of Coal-Research, Germany
Dear Dr. Glindemann:
Our inorganic and organometallic laboratory research needs often absolute clean and tight sealing of tapered joints on glass equipment.
Your PTFE-sealing rings proved to be a success while:
long term sealing of high vacuum equipment,
long term sealing of inert equipment until 200oC,
sealing of equipment and containers for synthesis and storage of dangerous (inflammable in air), oxygen sensitive and moisture sensitive chemicals,
sealing of equipment where contamination of reaction mixtures by joint grease has to be avoided.
Our group has gone over to use Glindemann-sealing rings instead of joint grease or PTFE-sleeves because of the amazing sealing properties and the advantages of working with greaseless joints.
(some extended information in the German version is not translated here)
We consider your PTFE-sealing rings as the present most advantageous way to work with greaseless and tight joints.

(signed by Andreas Bolte, 1997)

2. Test report of GLINDEMANN-PTFE-sealing rings for ground tapered joints
from: Professor Michael D. Fryzuk, Department of Chemistry, University of British Columbia, Canada
Dear Dr. Glindemann:
Thank you for the sample of your amazing o-ring seals. We have used Teflon sleeves in the past for certain situations but we have discontinued this practice because they are too expensive and not particularly effective. We have tested your o-ring seals using an extremely air-sensitive solution of {Co2TiCl}2ZnCl2 in toluene. This material is our indicator for O2 in our inert-atmosphere glove boxes since it goes from deep blue green to bright orange in the presence of 5 ppm of O2. A tube with 3 mL of this deep blue green solution was sealed with a stopper that had one of your seals and no grease inside an inert atmospheres glove box; the tube was then removed to the outside and inverted so that the solution was on top of the stopper. The colour could be seen to penetrate to the o-ring seal and no further. And amazingly, the solution remained blue green for many days. This tells me convincingly that this seal is airtight and robust. I would buy such a product because it is ideal for our research on air- and moisture-sensitive organometallic complex compounds.
M. D. Fryzuk
for <>; Tue, 10 Mar 1998 08:47:40 -0800

3. Test report of GLINDEMANN-PTFE-sealing rings.
from: Fan Ouyang, Beijing University of Aeronautics and Astronautics, April 24, 2003
My name is Fan Ouyang. I am a senior undergraduate at Beijing University of Aeronautics and Astronautics. I am now engaging in a new compound synthesis.
In our synthetic chain, there was a key link that should be reacted at high temperature (>110
) and high pressure (>8 Bar) for 12 hours. To realize the condition, we designed thick-wall glass tube to bear the high pressure, but in practice, we found the standard conical joints could not meet our hermetic requirement that a low-boiling-point reagent (5 ml) leaked completely in less than one hour.
Fortunately, in a journal, we saw the Glindemann-Sealing Ring. These sealing rings were designed for standarded conical joints that they are available for all joint calibers: NS 7,10,12,14,19,24,29,34,45,50,60,70.
We used the 19-sized sealing-ring. As it was described at the references, the sealing ring was very effective. Not only could it be used under high temperature, but also after 12 hours reaction with the high air pressure, the low-boiling-point reagent leakage rate was less than 10% (0.5ml/5ml).
Thanks to the Glindemann sealing-ring, our experiment finally got a complete success.
So I am glad to introduce this effective and convenient ring to my dear colleagues in China. Besides their excellent hermetic and vast application conditions, they can conveniently change a common joint into a hermetic joint so that it can save the investment on specialized equipment.

我叫欧阳凡,现在是北京航空航天大学大四学生。我现在正在合成一种新型化合物。在我们的合成路线中,有一个非常关键的步骤,需要在高温(>110)高压(>8个大气压)条件下反应12小时。 为达到这一目的,我们设计了厚壁的玻璃仪器来承受高压, 但是在实际操作中,我们发现标准磨口在我们的实验条件下不能达到要求的密封程度,一种低沸点的反应物(5ml)会在不到一小时完全泄漏。很幸运,在一本杂志上,我们发现了Glindemann密封环的广告。这种密封环是专门为标准磨口设计,型号有71012141924293445506070,可以应用于各种磨口。抱着试一试的心态,我们使用了19口的密封环。正如其产品说明中介绍的一样,这种密封环非常有效。其不但可以在高温下使用,而且在> 8个大气压的气压下反应十二小时后, 低沸点的反应物泄漏不超过10%0.5ml/5ml)。在这种密封环的帮助下,我们的实验最终取得了成功。 因此我很乐意向大家推荐这种密封环。 除了其优异的密封性能和广泛的使用条件,其最大的优点就是可以方便的使普通标准磨口达到很好的密封性,可以节约专门的密封设备的投资。这尤其适合中国的国情。

4. Test report of GLINDEMANN-PTFE-sealing rings.
from: Dr. Konstantin Chernichenko, University of Helsinki, Department of Chemistry, August 3, 2016
...I would like to express my gratitude to you for invention and commercialization of the rings. I hardly imagine my lab work without Glindemann rings, I use them not only for gas-tight reaction like hydrogenations, but for all the synthetic work I do and encourage students and colleagues to do same. In fact, I haven't been using any grease since I found out about the rings from a colleague some 7 years ago.

5. Opinion on GLINDEMANN-PTFE-sealing rings in the blogosphere.
from: an unknown user "mrj" at
"...21. mrj on May 31, 2008 10:53 PM writes... ... Glindemann sealing rings ( ... are just so superior to grease or teflon sleeves, there is no comparison. I don't use anything else for high vacuum work ... ."

6. Opinion on GLINDEMANN-PTFE-sealing rings by glassblower and author Gary S. Coyne.
Gary has been impressed by the ring as soon as he saw it back at the 2001 ASGS (American Scientific Glassblowers Society) symposium at Colorado Springs where we had a chance to meet personally after my oral lecture and presentation of my rings.
Glassblower Gary Coyne's joint-grease advices (download here), the now expired source link of which I made this copy was This note compares fluorinated greases such as Krytox®), Silicon greases and Hydrocarbon greases (such as Apiazon®). The author states "An alternative to stopcock greases is Teflon stopcocks, Teflon rotary valves (for high vacuum) and Teflon sleeves. If you need high vacuum and cannot use a standard Teflon sleeve, you may want to check out Teflon rings "
See also Gary's helpful book, written with the skills of a glassblower and with writing skills like a professor:
Gary S. Coyne. The Laboratory Companion: A Practical Guide to Materials, Equipment, and Technique.  Wiley-Interscience; Revised (18. November 2005) ISBN-10: 0471780863 ISBN-13: 978-0471780861. This book contains a chapter on the problems of jamming, leaking and sealing of glass joints of laboratory glassware. The book also compares all types of joint greases, and the tradeoff between typical problems of joint grease (high-vacuum, but only to the point ofleaching, contamination, degradation, aging) and of PTFE sleeves (Gary appreciates their chemical inertness but does not recommend sleeves for static vacuum). This tradeoff between disadvantages of joint grease and PTFE sleeves can be overcome by Glindemann-PTFE-sealing rings, that are both chemically inert and useful for high vacuum and static vacuum.

7. Opinion on GLINDEMANN-PTFE-sealing rings by Jim J. Brien, Business Development and Product Manager at Sigma-Aldrich company.
As a visitor at the 222nd ACS (American Chemical Society) National Meeting, Chicago, in 2001, I saw a person walking on the floor with a Sigma-Aldrich exhibitor badge, Mr. Jim Brien. I approached him and he tested my product sample, a conical joint glass stopper with my PTFE sealing ring, in a reagent tube with joint 14 mm. He noted, with surprise, that under amazingly little sealing force, and with an "nice elastic" feeling, this PTFE ring becomes transparent and visibly tight as if it was made of some soft material like grease. On the spot, Jim informed me about his managerial function and decided to add my product to the Aldrich catalogue.

Picture extracted from the Kimble/Kontes Website in the year 2001 showing Kontes product manager Mr. David Fenili promoting Glindemann rings on a pedestal. Originally, his predecessor Mr. Al Grubert introduced the rings into the Kontes catalogue after I demonstrated my product to him in 1998 during my work at the University of British Columbia in Vancouver, Canada. I met David Fenili and Al Grubert several times at exhibitions (ACS-Meetings and PITTCON 2001) were we distributed my product samples with great success at the Kimble-Kontes booth. I sold the product to Kontes, and they sold it to Aldrich from 2001 to 2009. Than we agreed that I sell the product directly to Sigma-Aldrich.
I was glad to meet these influential and technically informed persons.

 8. Handbook of Solvents, Volume 1. George Wypych, ChemTec Publishing - William Andrew Publishing, Toronto - New York - 2001. Chapter Experimental equipment and procedures for VLE-measurements (Vapor Liquid Equilibrium measurements). Page 160 "(...)The following problems have to be solved during the experiment: The equilibrium cell has to be sealed carefully to avoid any air leakage over the complete duration of the measurements (to measure one isotherm lasts about 14 days). Specially developed thin Teflon sealing rings were preferred to grease. (...)". 
Under these problematic conditions, sealing the glass taper joint with joint grease was no optimal option because absorbing solvent vapor would liquify the grease, resulting in glass contamination by leached grease, and the risk of a large gas leak. Using PTFE sleeves (which are chemically inert compared to grease) was no option, because no type of common PTFE sleeves can prevent air leakage and hold static vacuum constant with an error of less than 1 mbar for 14 days. This problem was solved by using Glindemann PTFE sealing rings that overcame the tradeoff between joint grease and PTFE sleeves.

9. Teaching book "Arbeitsmethoden in der Organischen Chemie", S. Hünig, G. Märkl, J. Sauer, P. Kreitmeier, A. Ledermann, 3. Auflage, Lehmanns Media, 2014 (Seite 39),   Citation:  "... Teflonhülsen ergeben mässig dichte Schliffverbindungen, die für einfache Apparaturen ausreichend sind.
Für höhere Ansprüche empfehlen sich dünne PTFE-Ringe (Glindemann-Ringe): Diese Dichtringe werden auf den Kernschliff aufgezogen in die Schliffhülse gesetzt und etwas angepresst. Wegen der kleinen Auflagefläche entsteht am Dichtring ein hoher Druck, der das PTFE fließen lässt. Die Stelle mit dem Dichtring erscheint bei richtiger Montage klar (wie bei einem gefetteten Schliff). Die so gedichteten Schliffverbindungen besitzen eine hervorragende Gas- und Vakuumdichtigkeit, lassen sich dabei aber leicht wieder trennen. Sie haben sich insbesondere bei Reaktionen mit sehr luft- und feuchtigkeitsempflindlichen Substanzen bewährt.
Translated: "Teflon sleeves result in moderately tight ground joints, which are sufficient for simple apparatus.
Thin PTFE rings (Glindemann rings) are recommended for higher demands: These sealing rings are pulled onto the ground joint, placed in the ground sleeve and pressed on slightly. Due to the small contact surface, high pressure is generated on the sealing ring, which allows the PTFE to flow. The spot with the sealing ring appears clear when installed correctly (like a greased section). The ground joints sealed in this way have excellent gas and vacuum tightness, but can be easily separated again. They have proven particularly effective in reactions with substances that are very sensitive to air and moisture."


Publications citing Glindemann-rings (use for Schlenk techniques) - Example uses of Glindemann-ring (PTFE sealing ring) for conical joint of Schlenk-flask with air- and moisture-sensitive chemicals, to exclude grease and improve cristallinization. Literature:

Chernichenko, K. et al. Hydrogen activation by 2-boryl-N,N-dialkylanilines: a revision of Piers’ ansa-aminoborane. Dalton Trans., 2012, 41, 9029-9032, DOI: 10.1039/C2DT30926B, see Electronic Supplementary Material file:

Chernichenko, K. et al. A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes. Nature Chemistry 5, 718–723 (2013), doi:10.1038/nchem.1693, see Electronic Supplementary Material file:

Chernichenko, K. et al. Metal-Free sp2-C–H Borylation as a Common Reactivity Pattern of Frustrated 2-Aminophenylboranes. J. Am. Chem. Soc., 2016, 138 (14), pp 4860–4868, DOI: 10.1021/jacs.6b00819, see Electronic Supplementary Material file:

Wipf, P. (2014) Techniques for Handling Air- and Moisture-Sensitive Compounds. See at .

Knudsen, B. P., Chorkendorff, I., & Stephens, I. (2016). Synthesis of Platinum Rare Earth Alloy Catalysts for Fuel Cells. Department of Physics, Technical University of Denmark.

Scott E. Denmark, Christopher R. Butler.
Vinylation with Inexpensive Silicon-Based Reagents: Preparation of 3-Vinyl-quinoline and 4-Vinylbenzophenone. Organic Syntheses, Vol. 86 (2009) 274-286.

Saleh et al. Chlorination of 1‑Carba-closo-dodecaborate and 1‑Ammonio-closo-dodecaborate Anions. Inorg. Chem. 2016, 55, 20, 10617-10627.

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