8-239 BUNA 90 B/U RING

Item HB90239 is a Buna-N NBR 90A Backup Ring built for anti-extrusion support behind O-rings in high-pressure hydraulic and pneumatic glands. The item is specified by AS568-239; 3.609 inch (91.67 mm) ID x 0.139 inch (3.53 mm) CS; 3.887 inch (98.73 mm) OD, with 3 5/8 inch nominal ID; 1/8 inch nominal CS for cross-reference against common gland and replacement dimensions. The Buna-N nitrile (NBR) compound is selected for oil, grease, fuel and general hydraulic fluid resistance in common industrial equipment. It is with a listed temperature range of -40°F (-40°C) to 250°F (121°C), which can help narrow material selection for heat, cold or process exposure. The black color and round profile provide a practical visual identifier during receiving, stocking and installation. As a backup ring, it works with a primary O-ring to help limit extrusion into clearance gaps under pressure. The each-unit format supports precise replacement, kitting, resale and job-specific purchasing. Key selection details include material, hardness, product type, cross-section, inside diameter, outside diameter and application. These specification details help customers and resellers compare the part by performance requirements rather than brand name alone.