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. Skived virgin PTFE (polytetrafluoroethylene) is a high molecular weight polymer and one of the most versatile plastics known to man. Virgin PTFE sheet can handle virtually all chemicals in the 0-14 pH range with the exception of molten alkali metals and elemental fluorine. It is suitable for service at temperatures from the cryogenic range up to 500deg F. This style is particularly recommended for applications in the food and beverage industry where high purity materials are required. It is also used where contamination or discoloration of flow media cannot be tolerated. Virgin PTFE is harder, and less conforming than restructured or expanded PTFE.