NPTF L1 plug is used to check an internal threaded hole. The NPTF L1 plug inspects the functional size or hand tight engagement of couplings or an internal thread. NPTF gages are used to inspect pipe threads that are used in Dryseal applications.

NPTF gages are manufactured per ANSI/ASME B1.20.5Screw the L1 plug into the fitting (hand tighten). This classifies the thread as to “Maximum”, “Basic”, or “Minimum”. NPTF (Dryseal) and ANPT (Aeronautical) thread tolerances are more closely controlled requiring an L3 gage as well as an L1.