8-440 BUNA 90 B/U RING

This Buna-N NBR 90A Backup Ring, item HB90440, is designed for buyers who need a clear specification match for anti-extrusion support behind O-rings in high-pressure hydraulic and pneumatic glands. The item is specified by AS568-440; 6.725 inch (170.82 mm) ID x 0.275 inch (6.99 mm) CS; 7.275 inch (184.79 mm) OD, with 6 3/4 inch nominal ID; 1/4 inch nominal CS for cross-reference against common gland and replacement dimensions. Its Buna-N nitrile (NBR) material provides 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. Common purchasing identifiers for this product include the material name, O-ring type, dimensional size, hardness and intended sealing application. Those attributes make the item easier to compare for maintenance, OEM production, MRO replacement and reseller catalog use.