Gasket material
Cork-Rubber Gasket Material
Cork-rubber is granulated cork bound in nitrile, neoprene or an SBR blend. It compresses like cork, recovers like rubber, and conforms to rough or warped faces at low bolt load, which is why it is the classic oil pan, cover, transformer and switchgear gasket. We cut it to your drawing on the waterjet.
- Family
- Cork granules in an elastomer binder
- Temperature
- -30 C to 110 C (-22 F to 230 F) in fluids
- Thickness
- 0.8 mm to 13 mm (about 1/32 in to 1/2 in)
- Formats
- Sheets 1.2 x 1.0 m and 1.2 x 1.2 m
- Designations
- ASTM F104 (F224000M2, F225000M2); MIL-C-6183 / SAE AMS-C-6183
- Product
- Sheet gaskets waterjet-cut to your drawing in Orange, California
Figures are the cited maker or standards values; the sheet datasheet and your application govern the final choice.
Every common gasket sheet material is quick for us to source, and we cut it to your print on our waterjet.
What cork-rubber seals
Cork-rubber is the gasket for covers that are stamped, cast or slightly warped, and for flanges where the bolt load is light. The cork granules crush into the low spots and the rubber binder holds the sheet together and gives it recovery [S2]. Mineral oil, transformer oil, gear oil and fuel are the media it is sold for; the nitrile-bonded grades resist petroleum oils and the MIL-C-6183 grades are specified for aromatic fuel and oil service [S1].
Keep it away from steam, hot water and pressure. The recommended system pressure on the Nebar® datasheet is 0.5 MPa, and the fluid temperature ceiling is 110 C [S2]. Above that, move to compressed fiber or solid rubber sheet.
Reading the callouts
Under ASTM F104 the first digit of the line callout is the material type [S3]. The Nebar sheet carries F224000M2 below 3 mm and F225000M2 at 3 mm and above [S2]. Military prints name MIL-C-6183 by type, class and grade; the document has been superseded by SAE AMS-C-6183 and the sheet is bought to that callout [S1]. Put the full callout on the drawing and the sheet is matched to it.
Specifications
Cork-Rubber specifications
| Property | Value (in / mm, C / F as stated) | Source |
|---|---|---|
| Composition | Granulated cork uniformly dispersed in a synthetic rubber compound (the MIL-C-6183 scope); nitrile-bonded below 3 mm, a neoprene/nitrile blend at 3 mm and above on the Nebar sheet | [S1, S2] |
| Hardness | 65 to 85 (ASTM D1415 test) below 3 mm; 65 to 80 at 3 mm and above | [S2] |
| Temperature, maximum in fluids | 110 C (230 F) | [S2] |
| Temperature, minimum | -20 C (-4 F) below 3 mm; -30 C (-22 F) at 3 mm and above | [S2] |
| Pressure | 0.5 MPa (5 bar, 73 psi), the maximum the Nebar datasheet recommends | [S2] |
| Thickness | 0.8 mm to 13 mm on the Nebar sheet; 1/8, 3/16 and 1/4 in listed as MIL-C-6183 grades | [S2, S4] |
| Formats | Sheets 1.2 x 1.0 m at 2.5 mm; 1.2 x 1.2 m at 3 mm and above | [S2] |
| Designations | ASTM F104 line callout F224000M2 below 3 mm and F225000M2 at 3 mm and above; MIL-C-6183 (superseded by SAE AMS-C-6183) for aromatic fuel and oil resistant gaskets | [S2, S1, S3] |
How we cut it
Gaskets are waterjet-cut to your drawing in Orange, California. Send a DXF, DWG or PDF with the thickness, the material or the specification callout, and the quantity. There is no die to build, so a single prototype and a repeat run go through the same setup, and a revision needs only a new file. The sheet comes from the sheet makers we buy from, to the callout on your print; the cutting is ours. Cork-rubber crumbles at sharp inside corners under a die; ask for a small radius on inside corners of the drawing and the waterjet holds it clean.
Where Cork-Rubber is used, and the usual alternatives
The print or the sheet datasheet governs; these are the sheets usually specified instead:
- Buna-N solid sheet: when the flange is machined flat and carries a bolted load with pressure behind it.
- Compressed non-asbestos fiber: when the joint runs hotter than 110 C or sees real pressure.
- Cellulose fiber: when a thin, low-cost paper-type gasket does the job in oil or water.
- Closed-cell sponge: when the lid seals against weather rather than oil.
Related gasket materials: Buna-N (Nitrile) Gasket Material, Compressed Non-Asbestos Fiber (CNAF) Gasket Material, Cellulose (Vegetable) Fiber Gasket Material, Closed-Cell Sponge Rubber Gasket Material. The full index is on the gaskets hub; send the drawing through request a quote.
Frequently asked
Is cork-rubber the same as cork-nitrile?
Cork-nitrile is cork-rubber with a nitrile binder, the common oil-resistant grade. Cork-neoprene and cork-SBR are the same idea with a different binder. Name the binder or the callout on the print.
What does MIL-C-6183 cover?
Vulcanized sheet of granulated cork in a synthetic rubber compound, for gaskets that need aromatic fuel or oil resistance. The military document is superseded by SAE AMS-C-6183, so new prints usually name the AMS version.
Can cork-rubber take hot water or steam?
No. The fluid temperature ceiling on the cited sheet is 110 C, and the material is sold for oils and fuels, not steam. Use EPDM or compressed fiber for water and steam.
Which thickness should I ask for?
The common cover-gasket thicknesses are 1/16 in, 3/32 in and 1/8 in. Thicker sheet conforms to rougher faces but needs more bolt load to hold. State the thickness on the drawing.
Do inside corners need a radius?
A small radius helps. Cork-rubber is weakest at a sharp inside corner, so a radius on the drawing gives the part a longer life in handling and service.
Sources
- [S1] MIL-C-6183B, Cork and Rubber Composition Sheet, for Aromatic Fuel and Oil Resistant Gaskets (superseded by SAE AMS-C-6183), EverySpec, https://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-C/MIL-C-6183B_9382/, accessed 2026-09-13.
- [S2] Nebar cork elastomer gasket material datasheet, James Walker (distributor-hosted copy), https://dobsongasket.com/images/pdf/JW_Nebar.pdf, accessed 2026-09-13.
- [S3] ASTM F104-11(2020), Standard Classification System for Nonmetallic Gasket Materials, https://store.astm.org/f0104-11r20.html, accessed 2026-09-13.
- [S4] MIL-C-6183 Cork & Rubber, Accurate Felt & Gasket, https://www.afgco.com/military-grade-cork-rubber, accessed 2026-09-13.
Nebar is a trademark of its owner. No affiliation or endorsement is implied.
Related guides
Send the Cork-Rubber gasket drawing and the quantity
Upload a DXF, DWG or PDF of the gasket with the quote request, or a photo of the part with a ruler if no drawing exists. Add the sheet thickness, the durometer or grade, the quantity and whether adhesive backing is wanted. Gaskets are cut in our own shop in Orange, California; a Conquest representative replies.
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