8-309 BLACK BUNA 90D BACK-UP RING

APG stocks the HB90309, an AS568-309 black Buna-N (Nitrile) 90 Shore A Back-Up Ring supplied with an inside diameter of 0.412 in (10.46 mm), a cross section of 0.21 in (5.33 mm), and an outside diameter of 0.832 in (21.13 mm). A back-up ring extends o-ring service life by supporting the seal against extrusion under high pressure.

The compound resists petroleum-based oils, propane and butane, and hydraulic fluids. That behavior comes from the compound itself: Buna-N (Nitrile) is known for reliable performance in both static and dynamic service, an economical choice for high-volume maintenance programs. The material carries a published service range of -40°F (-40°C) to 250°F (121.1°C). Applications involving polar solvents or strong acids call for a different compound.

Common environments for this compound include automotive, hydraulic and pneumatic systems, and general industrial maintenance.

Order part number HB90309, sold individually. Unit weight is approximately 0.535 g. Confirm chemical compatibility, pressure and temperature against your own application requirements before installing. APG can cross-reference from an existing part number, a drawing or a physical sample if this size is not an exact match.