NPTF L3 plug is used to check an internal threaded hole. The NPTF L3 plug inspects the wrench engagement and taper of couplings or internal threads and is used in conjunction or relationship with the NPTF L1.

NPTF gages are used to inspect pipe threads that are used in Dryseal applications Screw the L3 plug into the fitting (hand tighten). The gage must match the classification of the L1 plug within +/- 1/2 turns. NPTF (Dryseal) and ANPT (Aeronautical) thread tolerances are more closely controlled requiring an L3 gage as well as an L1.