8-138 BLACK BUNA 90D BACK-UP RING

Part number HB90138 is an AS568-138 black Buna-N (Nitrile) 90 Shore A Back-Up Ring measuring an inside diameter of 2.112 in (53.64 mm), a cross section of 0.103 in (2.62 mm), and an outside diameter of 2.318 in (58.88 mm). A back-up ring allows a standard o-ring to operate at higher pressures than it could unsupported.

The material holds up against greases and lubricants, hydraulic fluids, and many alcohols. That behavior comes from the compound itself: Buna-N (Nitrile) offers reliable performance in both static and dynamic service, low compression set under sustained load. The material carries a published service range of -40°F (-40°C) to 250°F (121.1°C).

Typical settings include automotive, general industrial maintenance, and hydraulic and pneumatic systems.

Reference part number HB90138 when ordering; the item is sold individually. Unit weight is approximately 0.6422 g and nominal inside diameter is listed as 2 1/8 inch. As always, verify media compatibility and operating conditions against the requirements of your specific application. APG can cross-reference from an existing part number, a drawing or a physical sample if this size is not an exact match.