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Gages Made to ANSI/ASME B1.20.1 1983
NPT (National Pipe Thread) plug gages are essential tools for inspecting the quality of threaded pipe fittings. Each type serves a specific purpose in the inspection process. Let's break down the differences between L1 Basic, L3 Basic, and 6-Step Crest Check NPT plug gages:
L1 Basic Plug Gage:
- Purpose: Primarily checks the pitch diameter of the thread at the hand-tight length of engagement (L1).Focus: Ensures the thread is within tolerance for proper mating and sealing.
L3 Basic Plug Gage:
- Purpose: Checks the taper and overall thread profile at the wrench-tight length of engagement (L3).
- Focus: Verifies that the thread has the correct taper and extends to the required length.
6-Step Crest Check Plug Gage:
- Purpose: Inspects the truncation limits and taper of the minor diameter.
- Focus: Assesses the sharpness of the thread crests and the consistency of the taper.
- Click HERE for Pitch Diameter Chart
Features:
- Gaging of NPT threads is quite easy and differs from straight threads in that only one gage, an L1 plug or L1 ring is used to determine acceptability.
- The taper pipe thread plug has a step at the L1 distance from its small end.
- When turned hand tight into the products internal pipe thread, (do not force the gage), the step is required to be flush with the large end of the product thread within a tolerance of plus or minus one turn.
- Special Note: Many times the product thread is chamfered, countersunk or recessed, exceeding the major diameter of the thread.
- In these instances, the gaging point of the product thread becomes where the first visible sign of a scratch mark at the major diameter occurs on the chamfer cone.
