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. Viton is the trade name for a fluoroelastomer that was developed by DuPont in 1957. 70 durometer fluorocarbon elastomers exhibit excellent resistance to high temperature and low compression set. They respond very well with resistance to ozone, high temperatures, oxygen, mineral oil, synthetic hydraulic fluids, fuels, aromatics and many organic solvents and chemicals. Gas permeability is very low and similar to that of butyl rubber. Special formulation can also improve resistance to water, steam, acids and fuels.