8-049 BLACK BUNA 90D BACK-UP RING

Ordered as HB90049, this is an AS568-049 black Buna-N (Nitrile) 90 Shore A Back-Up Ring with an inside diameter of 4.989 in (126.72 mm), a cross section of 0.07 in (1.78 mm), and an outside diameter of 5.129 in (130.28 mm). The back-up ring bridges the extrusion gap so the primary seal holds its shape under load.

The compound resists propane and butane, greases and lubricants, and hydraulic fluids. That behavior comes from the compound itself: Buna-N (Nitrile) is specified for strong abrasion and tear resistance, low compression set under sustained load. Published continuous service range is -40°F (-40°C) to 250°F (121.1°C). Verify compatibility before use with ozone and direct sunlight or polar solvents.

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

Reference part number HB90049 when ordering; the item is sold individually. Unit weight is approximately 0.875 g and nominal inside diameter is listed as 5 inch. Review your operating media and conditions against this specification before installation. APG can cross-reference from an existing part number, a drawing or a physical sample if this size is not an exact match.