The American Petroleum has standardized the underwater utilization of ring gaskets with the SRX and the SBX series rings. There is no dimensional difference between the standard RX and SRX or the BX and SBX. They will fit into their appropriate flange designated numbers. The "S" prefix identifies a gasket as having intersecting vent holes, allowing a pressure less metal-to-metal initial contact between the gasket and flange groove, while made up underwater. For pressure class ratings on these gaskets refer back to their non "S" type standard gasket classification chart for the RX-Series and BX-Series. Gaskets that have been torqued initiating a metal-to-metal seal should be discarded and not reused.