MSS - Manufacturers Standardization Society of the Valve and Fittings Industry.
Scope
"The purpose is to provide a Standard Practice for Excess Flow Valves installed in low pressure fuel gas piping systems which are designed to protect the appliance and its connections to the piping system by reducing the flow of gas should the flow in the line exceed some predetermined level. This Standard Practice applies to Excess Flow Valves used with gas fired appliances in Fuel Gas Distribution Systems with operating pressures between 5 inches water column (5""w.c.) and 14 inches water column (14""w.c.)."