Military & Aerospace O-Ring Specifications: The Complete Reference

This page is the full map of military and aerospace O-Ring specifications: every material spec and part standard you are likely to see on a drawing, current or legacy, what it means, what replaced it, and whether The O-Ring Store stocks it or quotes it. If a callout is not listed here, send it to us and we will run it down.

How to read a mil-spec O-Ring callout

Military and aerospace O-Rings are defined by two different kinds of documents, and most confusion comes from mixing them up:

• A material specification (MIL-R-83248, AMS7276, NAS1613, ZZ-R-765) defines the rubber itself: polymer family, hardness, fluid resistance, and the qualification tests a compound must pass.
• A part standard (M83248/1, MS28775, NAS1611, AS3209) defines the physical O-Ring: a table of dash sizes, each invoking a material spec.

A callout like M83248/1-214 reads as: part standard M83248 slash sheet 1 (75-duro fluorocarbon O-Rings), dash 214 (a 1" ID x 1/8" cross-section per AS568). On modern standards the dash number maps directly to the AS568 size; 900-series dashes are straight-thread boss (tube fitting) sizes. Look any dash up in the Master O-Ring Size Chart.

One more pattern worth knowing: most MIL specs were handed to SAE in the 1990s and became AMS documents, and many part standards later became AS documents. The old part numbers usually remain valid for procurement, which is why a 1971 callout still buys a part today.

Master lookup table

Temperature figures are the commonly quoted service ranges for the qualified compounds; the governing spec revision always controls. “Special quote” means we source it to order: send us the callout, size, and quantity.

Fluorocarbon (FKM): the M83248 family

The most-quoted mil-spec O-Ring family, filled with the FKM / Viton® compounds covered in our materials guide. The lineage runs MIL-R-25897 (1957, cancelled 1980) into MIL-R-83248, “Rubber, Fluorocarbon Elastomer, High Temperature, Fluid, and Compression Set Resistant.”

• Structure: Type I is O-Rings; Type II is sheet and molded shapes. Class 1 is 70 to 80 hardness (nominal 75); Class 2 is 85 to 95 (nominal 90).
• Compound callouts: M83248/1 covers Class 1 75-duro O-Rings, dashes /1-001 through /1-475 plus boss gaskets /1-901 through /1-932. M83248/2 covers Class 2 90-duro.
• Service: -20°F to +400°F (-29°C to +204°C), aircraft fuels, engine lubricants, and petroleum hydraulic fluids. Mil-spec FKM is black; commercial brown or green Viton® does not satisfy these callouts.
• Supersession: MIL-R-83248 went to SAE as AMS-R-83248, which was cancelled in 2005 and split. Materials: Class 1 became AMS7276 (active, rev J) and Class 2 became AMS7259 (active, rev F; note it is high-durometer FKM, not perfluoro, despite what some listings say). Parts: /1 O-Rings became AS3209, /1 boss gaskets AS3208, and /2 became AS3581. The M83248 part numbers remain in constant procurement use.
• Legacy numbers you may still see: AMS7278, AMS7279, and AMS7280 are older FKM ring specs (with part standards like AS3084/AS3085 and MS17413/MS9387/MS9388/MS9970), all functionally replaced by AMS7276 and AMS7259.

Stock: our Mil-Spec FKM 75 category covers the AS3209 / M83248/1 / AMS7276 callout family. 90-duro (M83248/2 / AS3581 / AMS7259) is a special quote.

Low-temperature FKM: M83485, AMS7287, AMS7379

Standard FKM stiffens near -20°F. Two active specs solve that:

• AMS7287 (Tg -22°F/-30°C, “GLT-type”): the successor to MIL-R-83485 and its M83485/1 part numbers; the current part standard is AS83485. Fuel, oil, and hydraulic service with real cold-soak capability.
• AMS7379 (Tg -40°F/-40°C, “GFLT-type”): -60°F to +400°F, part standard AS5729.

Both are special-quote items; include the fluid and the low-temperature requirement in your RFQ.

Perfluoroelastomer: AMS7257

AMS7257 covers FFKM (perfluoroelastomer) 70 to 80 hardness sealing rings for engine oil, fuel, and hydraulic systems beyond FKM’s temperature limit; qualified compounds run to roughly +600°F. There is no M-number scheme; parts are ordered by AS568 dash against the spec. Freudenberg’s Simriz® 501 and Z7257 are AMS7257 QPL materials made in NADCAP-certified production, with a +610°F high-temperature operating recommendation against the spec’s +554°F default; we stock Simriz® 501 and quote Z7257. See the full Simriz® FFKM lineup for the rest of the family.

Nitrile (NBR): hydraulic, fuel, and engine-oil families

Nitrile carries more mil callouts than any other polymer because it splits by fluid.

Petroleum hydraulic service (MIL-H-5606 systems)

The chain every hydraulic drawing eventually touches:

1. AN6227 and AN6230 (with MIL-P-5516 rubber): the WWII-era packings, rated only to +160°F, with their own sequential dash system. Long superseded but still requested.
2. MS28775 (material MIL-P-25732, now AMS-P-25732 / MIL-PRF-25732E): the classic -65°F to +275°F hydraulic O-Ring in AS568 dashes. Note the 2024 MIL-PRF-25732E revision retitled the service limit to 250°F while vendor charts still quote the legacy 275°F. Inactive for new design since 1989; parts continue as AS28775 for sustainment.
3. M83461/1 (material MIL-P-83461, now AMS-P-83461, active): the improved low-compression-set replacement, size-for-size with MS28775, qualified for both MIL-PRF-5606 and MIL-PRF-83282 fluids. This is the new-design hydraulic nitrile. M83461/2 covers the 900-series boss shapes.

Boss gaskets: MS28778

MS28778 (material MIL-P-5510, now AMS-P-5510) is the 90-duro straight-thread boss gasket that seals under the nut of MS33649/AS5202 ports. Its dash number is the tube size (-4, -6, -8…), not an AS568 dash. It superseded the legacy AN6290; parts continue as AS28778.

Fuel service

• MS29513 (O-Rings) and MS29512 (boss gaskets), material MIL-P-5315 (now AMS-P-5315): 60 to 70 duro low-temperature fuel nitrile for aviation gasoline and jet fuel, design range -65°F to +160°F. Parts continue as AS29513/AS29512. Our low-temp mil-spec Buna-N 70 category stocks this class of compound; confirm the exact callout on the product page or with us.
• MS9021 (O-Rings, about 320 sizes) and MS9020 (boss), material AMS7271: the engine-series fuel nitrile, -65°F to +200°F. MS9021 parts continue as AS3578. Note MS9021 is nitrile; it is sometimes mislabeled chloroprene.

Synthetic (diester) engine-oil service

• MS29561 (all sizes) and NAS617 (13 boss sizes), material MIL-R-7362 Type I (now AMS-R-7362): 70-duro nitrile qualified against MIL-PRF-7808 diester turbine oil, -65°F to +257°F. MS29561 parts continue as AS29561.
• AMS7272 is the companion engine-lube NBR ring spec (65 to 75 duro); manufacturer charts associate MS9241/MS9355 parts with it.

Fluorosilicone (FVMQ): the M25988 family

MIL-R-25988 (now MIL-DTL-25988; DoD has also adopted SAE AMS-R-25988) covers fluorosilicone: silicone’s low-temperature reach with fuel and oil resistance. Type 1 is O-Rings; classes split by capability and grades by durometer. The compound callouts:

Dash numbers are AS568 sizes, including 900-series boss sizes (M25988/1-910, etc.). Typical service for /1 compounds is roughly -70°F to +392°F depending on the qualified compound. Applications: aircraft fuel systems and diester-lubricant zones that see cold soak.

Stock: Fluorosilicone 70 Duro M25988/1 is on the shelf; /2, /3, and /4 are special quotes. We also stock commercial 75-duro FVMQ where a spec callout is not required.

Silicone (VMQ)

• MS9068 O-Rings (about 229 sizes), material AMS3304 (65 to 75 duro general-purpose silicone, -85°F to +401°F): for weather, ozone, and dry-heat service; not for fuels and not recommended for high-pressure dynamic use. Parts continue as AS3582.
• MS9385 / MS9386, material AMS7267 (75 duro, low compression set): hot-air system sealing rings, serviceable to +500°F in air.
• ZZ-R-765 (federal spec, superseded commercially by A-A-59588): the classic “Class 2b, Grade 70” commercial silicone callout; legacy parts include MS26577 (Class 2a Grade 60) and MS27290 (Class 2a Grade 50).

All silicone mil and federal callouts are special-quote items; our commercial silicone O-Rings cover unregulated service.

Ethylene propylene (EPR/EPDM): NAS1613 for Skydrol

Phosphate-ester hydraulic fluids (Skydrol®, HyJet®) destroy nitrile and FKM (see the Chemical Compatibility matrix). The aerospace answer is NAS1613, “Packing, Preformed, Ethylene Propylene Rubber,” an 80-duro EPR/EPDM qualified for -65°F to +250°F (with short excursions higher).

• NAS1611: the standard-size O-Ring series (about 249 AS568 dashes), NAS1613 Class 1.
• NAS1612: the boss/tube-fitting sizes (900 series), NAS1613 Class 2.
• Revision matters: NAS1613 Rev 2 and Rev 6 (“Code A”) are both quoted today. Rev 6 adds longer fluid soaks, a harsher dynamic endurance profile, and additional phosphate-ester fluids, so a Rev 6 requirement is stricter than Rev 2. State the revision on your RFQ.

Stock: our Simrit® E454 peroxide-cured EPDM 80 category (Simrit® is a Freudenberg Sealing Technologies brand) serves NAS1611-size phosphate-ester service; confirm the required NAS1613 revision with us before ordering for a certified application.

Callouts that trip people up

• AS3209 vs AMS3209: AS3209 is the FKM 75-duro O-Ring part standard (AMS7276 material). AMS3209 is a weather-resistant chloroprene material spec used for electrical-connector O-Rings. Same digits, different worlds.
• AMS7259 is not perfluoro. It is 90-duro FKM, the M83248/2 successor. The FFKM spec is AMS7257.
• MS9021 is nitrile (AMS7271 fuel grade), despite occasionally being listed as chloroprene.
• NAS1611/NAS1612 are EPR, for phosphate-ester fluids only. Petroleum fluids will swell them; do not substitute for MS28775-type nitrile.
• MIL-G-21569 is a Navy diesel cylinder-liner seal spec (Class 1 nitrile, Class 2 silicone), not a butyl O-Ring spec. There is no dedicated active military butyl O-Ring material spec; butyl is bought to ASTM D2000 callouts. See Butyl.
• MIL-R-6855 / MIL-PRF-6855 is a general molded-rubber goods spec (Class 1 oil-resistant NBR, Class 2 weather-resistant CR). It appears on drawings for custom molded seals, not standard-size O-Rings.

Legacy-to-current cross-reference

If your drawing says the left column, today you procure the right:

Stocked vs special quote at The O-Ring Store

On the shelf today:

• Mil-Spec FKM 75 Duro: AS3209, M83248/1, AMS7276
• Fluorosilicone 70 Duro: M25988/1
• Low-Temp Mil-Spec Buna-N 70 Duro (MS29513-class fuel service)
• Simrit E454 EPDM 80 Duro (NAS1611-size phosphate-ester service)

Everything else on this page is a special quote. That is normal in this world: much mil-spec hardware is made to order with certs. Send us the full callout (for example “M83461/1-214, NAS1613 Rev 6, or AMS7379 / AS5729-012”), the quantity, and any documentation requirement (CoC, cure date, test reports), and we will quote compound, price, and lead time. See also Certificate of Conformance, cure date, and lot traceability, all backed by our ISO 9001:2015 system.

Request a mil-spec quote

Sources and further reading

• Spec status and supersessions verified against SAE, DLA/ASSIST, and EverySpec records as of July 2026. The governing document is always the current revision cited in your contract or drawing.
• Compound behavior behind these specs: Freudenberg FST 2025 Technical Manual (ch. 2 Materials, ch. 6 Static Seals), the reference base for this handbook’s Materials, Chemical Compatibility, and Design & Engineering sections.
• Related handbook pages: Nitrile · FKM / Viton® · Fluorosilicone · Silicone · EPDM · FFKM · Butyl · Sizing & AS568 · Master Size Chart · CoC, cure date & lot traceability