InSeal stocks a range of standard size nitrile o rings. Specials can also be supplied to order Nitrile rubber is also known as Buna-N, Perbunan, or NBR rubber. Nitrile o rings are used in the prescence of fats, oils, fuels, and other liquids contaminated by these; they can also be used at a range of temperatures (-40c to +120c depending on grade).