IF‐ Internal Flush Connections are Rotary Shoulder Connections having the V‐038R Thread Forms. Gauging practice and thread inspection should conform to the requirements of API Spec 7‐2. Thread Check, Inc. offers the complete range of API IF ‐ Internal Flush Thread Plug and Ring Gages to API Spec 7‐2. Our engineering staff have served on various API gaging subcommittees and have worked in the energy industry for many decades. Thread Check's expert engineers can assist you with engineering and building custom gages. Thread Check is a proud member of the American Petroleum Institute.