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.
Ethylene Propylene Specs:
- ASTM D 1418 Designations: EP, EPM, EPDM
 - ASTM D 2000, SAE J200 Type/Class: AA, BA, CA, DA
 - General Temperature Range: -65 to +300 Degrees (F)
 
FKM Performs Well In:
- Alcohols
 - Automotive brake fluids
 - Dilute acids & dilute alkalies
 - Ketones (MEK, acetone)
 - Silicon oils & greases
 - Steam (up to 400 F, 204 C)
 - Water
 
EPM Does Not Perform Well In:
- Aliphatic & aromatic hydrocarbons
 - Di-ester based lubricants
 - Halogenated solvents
 - Petroleum oils