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ANSI/MSS SP-25-2018
Standard Marking System for Valves, Fittings, Flanges, and Unions
This standard marking system applies to the marking of new valves, fittings, flanges, and unions used in piping connections that include (but are not limited to) flanged, soldered, brazed, threaded, or welded joints.
Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. [mss]