8-255 BLACK BUNA 90D BACK-UP RING

This back-up ring is supplied in AS568-255 black Buna-N (Nitrile) 90 Shore A built to an inside diameter of 5.609 in (142.47 mm), a cross section of 0.139 in (3.53 mm), and an outside diameter of 5.887 in (149.53 mm), catalogued under part number HB90255. It installs on the low-pressure side of an o-ring to prevent extrusion into the clearance gap at elevated pressure.

Expect good resistance to hydraulic fluids, petroleum-based oils, and many alcohols. That behavior comes from the compound itself: Buna-N (Nitrile) delivers low compression set under sustained load, strong abrasion and tear resistance. Published continuous service range is -40°F (-40°C) to 250°F (121.1°C). Verify compatibility before use with ozone and direct sunlight or polar solvents.

Typical settings include construction equipment, agricultural equipment, and general industrial maintenance.

Stocked as HB90255 and sold individually. Unit weight is approximately 2.0809 g. Confirm chemical compatibility, pressure and temperature against your own application requirements before installing. Not finding the exact configuration you need? APG cross-references from prints, samples and competitor part numbers.