This Standard covers non-metallic flat gaskets. It offers comprehensive solutions applying to materials, dimensions, tolerances and marking. B16.21 addresses gaskets that are dimensionally suitable for use with flanges described in reference flange standards ASME B16.5, ASME B16.47, API Specification 6A, and ISO 10423 as well as with other ASME standards, such as the Boiler and Pressure Vessel Code and the B31 Piping Codes.