Viton® (FKM) O-Rings

What FKM is, and whether Viton is the same thing

FKM is the ASTM D1418 designation for fluoroelastomers, the family of fluorine-containing rubbers used where a seal meets oil, fuel or solvent at elevated temperature. Viton is a polymer trademark owned by The Chemours Company; a molder buys the raw polymer and compounds it, so "genuine Viton" on a print fixes where the polymer came from, not who made the ring. A print that says FKM accepts any qualified fluoroelastomer compound. FPM is the same material in older European usage, and FFKM (perfluoroelastomer) is a separate, costlier family covered on the FFKM page.

FKM grades by designation

The letters after the trade name are the polymer maker's grade families. They differ in monomer mix, fluorine content and cure system; the compound datasheet names the grade, while most prints name only FKM and a hardness, or an AMS document. The temperature figures below are the Parker O-Ring Handbook (ORD 5700) family range, and a grade's own datasheet governs.

Grade descriptions are qualitative and follow the polymer maker's nomenclature; they are not a compatibility rating. The chemical compatibility guide covers the media, and the quote names the compound your print or your engineering specifies and sends its datasheet.

Viton O-ring specifications

Military and AMS callouts that specify FKM

Aerospace and OEM prints rarely say "Viton"; they name a material document, and the document status matters because the military originals are cancelled while parts are still ordered by the old numbers. The statuses below are read from the DLA ASSIST and SAE Mobilus records (read 2026-09-06).

The dash number after the slash sheet is the AS568 size, so an M83248/1-214 is a fluoroelastomer ring in size -214: the AS568 size chart carries the dimensions, and the M83248, AMS7276 and AMS7280 guides decode the documents. Parts to these documents are made by manufacturers on the relevant qualified products list; Conquest supplies them with the certificate of conformance and, where the order calls for it, AS9102 first-article documentation.

Where Viton O-rings work, and where they fail

Sizes and forms we supply

All 369 AS568 sizes (349 general-purpose dash sizes plus the 20 boss-seal sizes) and the ISO 3601 metric series, in the durometers listed above; O-ring cord for rings spliced and vulcanized by the maker in odd diameters (static service only); and X-rings and backup rings in the same families. The AS568 chart and the metric chart carry the dimensions, and the dash number guide explains the numbering.

How FKM compares with its neighbors

Where Viton fits

Where the medium is petroleum-based or chemically aggressive and the temperature exceeds what nitrile handles; the nitrile vs FKM comparison draws that line. For steam or brake fluid, EPDM (see EPDM vs FKM); for dry heat with no oil, or extreme cold, silicone (see FKM vs silicone); for ketones, amines and the most aggressive streams, FFKM (see FFKM vs FKM). A specification's temperature limit is a test condition, not an operating limit; the compound datasheet governs. A certificate of conformance ships with every order; the cure date is on the label, and the shelf-life guide explains how both are read.

Sources: Parker O-Ring Handbook ORD 5700, section 2.2, read 2026-09-14; ASTM D1418; ASTM D2000; AS568; ISO 3601; DLA ASSIST document details for MIL-R-83248, MIL-R-83248/1, MIL-R-83248/2, SAE-AMS7276, SAE-AMS7259 (read 2026-09-06); SAE Mobilus pages for AMS7287, AMS-R-83248, AS83248/1, AS3208, AS3209, AS3581 (read 2026-09-06); 21 CFR 177.2600.

Parker is a trademark of Parker Hannifin Corporation. Viton is a trademark of The Chemours Company; Aflas is a trademark of AGC. No affiliation or endorsement is implied.

Reviewed by Grant Midstokke, Conquest Seal Corporation. Last updated September 2026. Material ranges are the published references named beside them; the compound datasheet and your application govern the final choice.