Ordered as H4X51, this is a black Buna-N (Nitrile) 70 Shore A O-Ring built to an inside diameter of 51 mm (2.008 in), a cross section of 4 mm (0.157 in), and an outside diameter of 59 mm (2.32 in). The o-ring creates a positive seal at flange, piston and rod interfaces without added hardware.
It resists hydraulic fluids, greases and lubricants, and petroleum-based oils. That behavior comes from the compound itself: Buna-N (Nitrile) is known for low compression set under sustained load and an economical choice for high-volume maintenance programs. Published continuous service range is -40°F (-40°C) to 250°F (121.1°C). Applications involving strong acids or ozone and direct sunlight call for a different compound.
Maintenance and OEM teams specify it across general industrial maintenance, hydraulic and pneumatic systems, and fluid power.
Stocked as H4X51 and sold individually. Unit weight is approximately 2.7533 g. As always, verify media compatibility and operating conditions against the requirements of your specific application.
Description 4MM CS X 51MM ID BLACK BUNA 70D
Actual Outside Diameter 59 mm (2.32 inch)
Actual Cross Section 4 mm (0.157 inch)
Actual Inside Diameter 51 mm (2.008 inch)
Measurement System Metric
Product Category O-Rings - Metric - Commodity