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.
Chloroprene (Neoprene) Specs:
- ASTM D 1418 Designations: CR
 - ASTM D 2000, SAE J200 Type/Class: BC, BE
 - General Temperature Range: -40 to +250 Degrees (F)
 
CR Performs Well In:
- High aniline point petroleum oils
 - Mild acids
 - Refrigeration seals (resistance to Freon & ammonia)
 - Silicon oil & grease
 - Water
 
Silicone Does Not Perform Well In:
- Hydrocarbons (aromatic, chlorinated, nitro)
 - Ketones (MEK, acetone)
 - Phosphate ester fluids
 - Strong oxidizing acids