Fits at the top of the thread of standard male o-ring boss fittings to create a seal. Made of nitrile rubber (NBR). The most widely used O-Ring elastomer. Excellent resistance to petroleum products. Excellent compression set, tear and abrasion resistance. Does not have good resistance to ozone, sunlight, or weather, unless specifically compounded. Should not be stored in direct sunlight or near motors or other electrical equipment which may generate ozone.