O-Rings are round rubber washers that are placed around the valve stem in order to create a seal, preventing leaking from occurring and providing an excellent resistance to vibration. The listed size is referenced from AS568 dimensions, which is the Aerospace Size Standard for O-rings from the Society of Automotive Engineers.
Fluorocarbon (Viton) Specs:
- ASTM D 1418 Designations: FKM, Viton
 - ASTM D 2000, SAE J200 Type/Class: HK
 - General Temperature Range: -15 to +400 Degrees (F)
 
FKM Performs Well In:
- Acids
 - Aircraft engine applications
 - Gasoline (alcohol blends)
 - Hard vacuum applications
 - Low outgassing applications
 - Petroleum products
 - Silicon fluids & greases
 - Solvents
 
FKM Does Not Perform Well In:
- Amines
 - Hot chlorosulfonic acid
 - Hot hydrofluoric acid
 - Hydrocarbons (nitro)
 - Ketones
 - Low molecular weight esters & ethers
 - Fireproof hydraulic fluids (e.g. Skydrol)