8-378 BLACK BUNA 90D BACK-UP RING

APG stocks the HB90378, an AS568-378 black Buna-N (Nitrile) 90 Shore A Back-Up Ring measuring an inside diameter of 10.475 in (266.07 mm), a cross section of 0.21 in (5.33 mm), and an outside diameter of 10.895 in (276.73 mm). A back-up ring installs on the low-pressure side of an o-ring to prevent extrusion into the clearance gap at elevated pressure.

This material stands up to petroleum-based oils, many alcohols, and propane and butane. That behavior comes from the compound itself: Buna-N (Nitrile) is specified for reliable performance in both static and dynamic service, strong abrasion and tear resistance. Service temperature is rated from -40°F (-40°C) through 250°F (121.1°C).

You will find this material specified across agricultural equipment, fluid power, and construction equipment.

Order part number HB90378, sold individually. Unit weight is approximately 8.8541 g. Confirm chemical compatibility, pressure and temperature against your own application requirements before installing.