2-1/2in Full Face Flange Gasket — Red Rubber 150#/125#, 1/8in Thick, 7in OD

A 2-1/2 inch full face gasket in 1/8 in. red rubber, cut to ASME B16.21 for 150 lb flanges. Pipe size is a name, not a measurement — 2-1/2 in. pipe is 2-7/8 in. across the outside, which is why the bore reads 2-7/8 in. and the outer edge 7 in.

Fits 150 lb steel and 125 lb cast iron flanges — Class 125 and Class 150 share the same bolt pattern, so one gasket covers both. A Class 300 flange is wider on a different bolt circle and takes a different gasket. Red rubber (SBR) suits water, brine, air and low-pressure service; for oil, fuel, solvents or acids ask for Buna, Viton, EPDM or non-asbestos.

Where a 2-1/2 in. goes. Fire sprinkler and standpipe risers, where 2-1/2 in. is a standard line size, plus small pump flanges, booster sets and HVAC branch lines. Like the 5 in., it is a size most pipe runs skip — which is exactly why the gasket can be hard to track down when you do need one. Four bolts on a 5-1/2 in. circle; the 3 in. is the same four bolts on a 6 in. circle, so check the circle rather than the hole count.