568-428 BUNA 70 SQUARE CUT RINGS

APG stocks the SH70428, an AS568-428 black Buna-N (Nitrile) 70 Shore A Square-Cut Ring with an inside diameter of 4.85 in (123.19 mm), a cross section of 0.275 in (6.99 mm), and an outside diameter of 5.4 in (137.16 mm). A square-cut ring seals with a broad flat contact band instead of the line contact of a round-section ring.

The compound resists water, greases and lubricants, and hydraulic fluids. That behavior comes from the compound itself: Buna-N (Nitrile) is specified for low compression set under sustained load, strong abrasion and tear resistance. The material carries a published service range of -40°F (-40°C) to 250°F (121.1°C). It is not the right choice where polar solvents or ozone and direct sunlight are present. The profile itself contributes a flat contact band that spreads sealing load across a wider area and a rectangular section that will not roll in the groove. Note that a square section is less suited to high-speed rotary service, where the larger contact area raises friction and heat.

It sees regular use in fluid power, automotive, and hydraulic and pneumatic systems.

Reference part number SH70428 when ordering; the item is sold individually. Nominal inside diameter is listed as 4 7/8 inch. Check the compound against your process media, pressure and temperature before committing to a design. For a size or compound outside the standard catalog, APG can quote from a print or sample.