- Family
- FVMQ (fluorosilicone)
- Standard range
- -73 C to 177 C (Parker® O-Ring Handbook ORD 5700)
- Durometers
- 60, 70, 75 and 80 Shore A: the Parker compounds the handbook pairs with the AMS-R-25988 grades (LM158-60, LM159-70, L1077-75, LM160-80; Tables 8-3 and 8-4)
- Standards
- ASTM D1418 FVMQ; SAE AMS-R-25988 (M25988/1 to /4)
- Product
- O-rings in AS568 and ISO 3601 sizes, quoted in the compound the print names
Service temperatures here are the family figures published in Parker O-Ring Handbook ORD 5700A/US §2.2; the compound datasheet and your application govern the final choice.
Larger and non-standard sizes: an O-ring beyond the molded size lists can be supplied as a spliced and vulcanized O-ring, which the maker joins from cord of the same compound. That page lists, family by family, which makers offer the compound as cord, and what to send for a quote.
Fluorosilicone O-rings (FVMQ) give silicone's temperature range with fuel and oil resistance: the Parker O-Ring Handbook (ORD 5700) rates the family from -73 C (-99 F) to 177 C (351 F), and it is the aerospace fuel-system seal material behind AMS-R-25988 and the M25988 part numbers. Like silicone it is a static seal material. Conquest supplies fluorosilicone O-rings in AS568 and metric sizes, including compounds made to the M25988 slash sheets by qualified manufacturers.
Fluorosilicone O-ring specifications
| Property | Value | Source |
|---|---|---|
| Continuous service temperature | -73 C to 177 C (-99 F to 351 F) | Parker ORD 5700 |
| Material designation | FVMQ under ASTM D1418 | ASTM naming |
| Aerospace specification | SAE AMS-R-25988 (current revision B, June 2023; SAE's record also lists a cancellation in August 2017, before that revision): M25988/1 (70 A), /2 (75 A), /3 (60 A), /4 (80 A) | SAE AMS-R-25988B record (SAE Mobilus) and DLA ASSIST record, read 2026-09-24 and 2026-09-27; grade hardness per Parker ORD 5700 Table 8-3 |
| Service | Static seals only | Parker ORD 5700 |
| Gland note | Cut the tabulated extrusion clearance by 50 percent, as for silicone | Parker O-Ring Handbook ORD 5700, section 4.2 |
Sizes and forms we supply
Every AS568 size, the general-purpose dash sizes and the boss-seal sizes alike, 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.
Where fluorosilicone O-rings work, and where they fail
| Medium or condition | Verdict | Note (Parker O-Ring Handbook ORD 5700) |
|---|---|---|
| Aircraft and automotive fuels at low temperature | Excellent | The core application |
| Petroleum oils, aromatics | Good | Silicone's range with fuel resistance |
| Extreme cold | Excellent | Flexible to -73 C |
| Dry heat to 177 C | Good | Hot air resistance worse than silicone |
| Ozone, weather | Excellent | Saturated backbone |
| Dynamic service | Not recommended | Low tear strength; static only |
| Steam, brake fluid, ketones | Not recommended | EPDM |
Typical applications
Aircraft fuel-system fittings, fuel-quantity probes and fuel-pump static seals to the M25988 sheets; military and general-aviation ground-support equipment; automotive fuel-injection and evaporative systems; and any static fuel or oil seal that must survive cold soak below the range of standard fluorocarbon.
Where fluorosilicone fits
Fuel-system seals that must stay flexible in the cold, where Viton® stiffens and silicone swells. Above 177 C or in dynamic service, Viton is the usual fit; the fluorosilicone vs FKM guide compares the two. The silicone guide covers the family and the mil-spec chart the M25988 part numbers.
Sources: AMS-R-25988; AS568; ASTM D1418; ISO 3601; ORD 5700; Parker O-Ring Handbook; SAE AMS-R-25988B record (SAE Mobilus) and DLA ASSIST record, read 2026-09-24; Parker O-Ring Handbook ORD 5700, Tables 8-3 and 8-4, read 2026-09-24; SAE Mobilus current-revision records (AMS-R-25988B citation line), read 2026-09-27; DLA ASSIST record for MIL-DTL-25988, read 2026-09-24; Parker O-Ring Handbook ORD 5700, section 4.2.
Parker is a trademark of Parker Hannifin Corporation. Viton is a trademark of The Chemours Company. No affiliation with or endorsement by either trademark owner is implied.
Frequently asked
Is fluorosilicone the same as silicone?
Same backbone with fluorine on the side chains, which adds fuel and oil resistance; static-only like silicone.
What does M25988/1-214 mean?
A 70 A fluorosilicone O-ring to AMS-R-25988 class 1, in the AS568-214 size; /2, /3 and /4 are the 75, 60 and 80 A sheets.
Was AMS-R-25988 cancelled?
SAE's record lists a cancellation in August 2017, and SAE then issued revision B in June 2023, the current revision. The government's MIL-DTL-25988 base document is inactive on the DLA ASSIST record (2025). Order to the revision the print names.
Orders are handled under Conquest Seal's AS9100D quality management system, whose certificate scope includes distribution.
Send the part number and the quantity for Fluorosilicone
The AS568 dash number or the inside diameter and cross-section, the durometer, the quantity, the medium and temperature, and any specification the print names. A Conquest representative replies. Quotes answered within one business day. A person answers (714) 632-9830, Pacific business hours.
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