8-439 BLACK BUNA 90D BACK-UP RING

Ordered as HB90439, this is an AS568-439 black Buna-N (Nitrile) 90 Shore A Back-Up Ring measuring an inside diameter of 6.475 in (164.47 mm), a cross section of 0.275 in (6.99 mm), and an outside diameter of 7.025 in (178.44 mm). The back-up ring bridges the extrusion gap so the primary seal holds its shape under load.

Expect good resistance to propane and butane, water, and greases and lubricants. That behavior comes from the compound itself: Buna-N (Nitrile) is known for 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). Exposure to automotive brake fluid or polar solvents will shorten service life.

Typical settings include agricultural equipment, general industrial maintenance, and fluid power.

This item is sold individually under part number HB90439. Unit weight is approximately 11.52 g. Review your operating media and conditions against this specification before installation. Not finding the exact configuration you need? APG cross-references from prints, samples and competitor part numbers.