Chemical resistant elastomer.
Fuel compatible.
230 °C service.

Buna-N (nitrile): cheap, good fuel/oil resistance at moderate temperature, -40 to +120 °C service. Standard for consumer automotive fuel. Viton (FKM): premium cost, better resistance to aggressive fuels (E85 ethanol, biodiesel, ultra-low sulfur diesel), higher temperature (230 °C), better fuel-aging. For modern automotive with biofuels or under-hood elevated temperature: FKM. For basic fuel systems at moderate temperature: NBR. Automotive is transitioning FKM for mandatory standards.

FFKM (perfluoroelastomer — Kalrez, Chemraz): $200-500 per small O-ring. FKM: $1-10. Justify FFKM when: (1) aggressive chemistry FKM can't handle (amines, specific solvents, concentrated oxidizers), (2) high-purity semiconductor applications, (3) maximum chemical certainty for critical sealing. For most applications, FKM is adequate. FFKM is specialty premium material.

Standard FKM: -20 to +230 °C continuous. Short-term to +260 °C. Low-temp grades (GLT, GBL): -40 °C capable but reduced chemical resistance. For service below -40 °C, FKM becomes brittle — use silicone or HNBR. For service above 230 °C, use FFKM (up to 316 °C) or specialty elastomers.

Stock AS568 and BS-2951 inch and metric O-ring sizes in Viton 75A and 90A durometer, black color. Immediate availability: diameter 1 mm to 500 mm, cross-section 0.5 mm to 20 mm. Custom sizes: 2-4 week lead time depending on volume. For special shapes (T-seals, custom gaskets): mold tooling required.

Compression mold tool: $3,000-15,000 depending on part size and complexity. Transfer mold: $8,000-25,000. Injection mold: $15,000-50,000 for production volumes. Tool amortizes over production volume — for 10,000+ parts, tool cost is negligible per part. For prototype or low volume, machining from sheet or standard compound slabs may be more economical.

Standard O-rings: in stock. Custom FKM parts: compression molding 3-4 weeks after tool, injection 1-2 weeks after tool. Tool lead time: 3-6 weeks. First production run: 6-10 weeks from design approval. Sample parts for testing: 4-5 weeks typical. For rush, aluminum rapid-prototype tooling can cut 2-3 weeks from timeline at slight cost premium.