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.
Nitrile (Buna N) Specs:
- ASTM D 1418 Designations: NBR, XNBR
 - ASTM D 2000, SAE J200 Type/Class: BF, BG, BK, CH
 - General Temperature Range: -40 to +225 F
 
NBR Performs Well In:
- Petroleum oils & fuels
 - Silicon oils & greases
 - Ethylene glycol
 - Dilute acids
 - Water (Below 212 F)
 
NBR Does Not Perform Well In:
- Aromatic hydrocarbons (toluene, xylene, benzene)
 - Automotive brake fluid
 - Halogen derivatives (carbon tetrachloride, trichloroethylene)
 - Ketones (acetone, MEK)
 - Phosphate ester hydraulic fluids (Skydrol, Pydraul)
 - Strong acids