Npt threadsizes

Because of allowable tolerance of plus or minus one turn on both the male and female threads, the actual thread engagement length / threads of the assembly will vary from the engagement dimensions shown in the chart which are based on “perfect” threads.

Npt threadchart

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ANSI B1.20.1 Standard provides both “Hand Tight” engagement (L1) and “Wrench Make-Up” (L3) dimensions. The L1 basic hand tight engagement applies to NPTF threads. It is the theoretical length of assembly (hand-tight) if both parts had perfect thread form and taper and were exactly at the nominal size. The diagram and table below show standard L1 lengths (Hand-Tight Engagement) for pipe threads as well as the L3 (Wrench Make-Up). For convenience we have added L1 + L3 which is the total thread engagement when wrench tight.