0.219" Thick, Square Cross Section Buna-N, also known as nitrile rubber (NBR), is made of a synthetic rubber that has anti-microbial properties and is resistant to chemicals, oils, solvents, greases and petroleum-based fluids. It is resistant to abrasions, cuts, punctures, slashes and snags.|Square cross-section shapes offer good high pressure seals, but are best used in static applications. They can be used as a direct replacement for a round O-ring.