8-253 BLACK BUNA 90D BACK-UP RING

Part number HB90253 is an AS568-253 black Buna-N (Nitrile) 90 Shore A Back-Up Ring supplied with an inside diameter of 5.359 in (136.12 mm), a cross section of 0.139 in (3.53 mm), and an outside diameter of 5.637 in (143.18 mm). A back-up ring extends o-ring service life by supporting the seal against extrusion under high pressure.

Buna-N (Nitrile) delivers strong abrasion and tear resistance, low compression set under sustained load. It resists hydraulic fluids, water, and petroleum-based oils. Service temperature is rated from -40°F (-40°C) through 250°F (121.1°C). It is not the right choice where strong acids or ketones are present.

Maintenance and OEM teams specify it across hydraulic and pneumatic systems, automotive, and agricultural equipment.

HB90253 ships individually. Unit weight is approximately 1.979 g and nominal inside diameter is listed as 5 3/8 inch. Review your operating media and conditions against this specification before installation. APG supports cross-referencing from drawings, samples and competitor numbers when a listed size is not an exact fit.