-257 BLACK BUNA 70D O-RING

H70257 is an AS568-257 black Buna-N (Nitrile) 70 Shore A O-Ring measuring an inside diameter of 5.859 in (148.82 mm), a cross section of 0.139 in (3.53 mm), and an outside diameter of 6.137 in (155.88 mm). In service, this o-ring seats in a machined groove and forms a leak-tight barrier when compressed between two mating surfaces.

Buna-N (Nitrile) is specified here for low compression set under sustained load and most widely specified general-purpose sealing elastomer. The compound resists propane and butane, petroleum-based oils, and greases and lubricants. The material carries a published service range of -40°F (-40°C) to 250°F (121.1°C). It should not be specified for service in strong acids or polar solvents.

Maintenance and OEM teams specify it across hydraulic and pneumatic systems, fluid power, and construction equipment.

Order part number H70257, sold individually. Unit weight is approximately 5.7207 g and nominal inside diameter is listed as 5 7/8 inch. Confirm chemical compatibility, pressure and temperature against your own application requirements before installing. If you need a size, durometer or compound that is not listed, APG can cross-reference from a print, a sample or a competitor part number.