Ring gaskets are a flat sealing element, consisting of an inner and outer diameter sized to fit a flange's bore and bolt circle. Ring gaskets sit inside the flange's bolt circle. ASME B16.21 and ASME B16.47 govern the dimensions of ring gaskets for standard and large diameter pipe flanges. 75 durometer SBR rubber is a synthetic polymer, commonly known as "Red Rubber". SBR is a copolymer of styrene and butadiene and has properties similar to natural rubber. It is a widely used because it is inexpensive and has the ability to deform to uneven flange edges. SBR has excellent impact-strength, abrasion resistance, heat resistance, and sustains flexibility at lower temperatures. Even though SBR is not resistant to oil, gasoline, and hydrocarbon solvents, it performs well in industrial applications which involve contact with chemicals, water, air and steam.