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PIPE RING GAGES

There are two (2) basic styles of screw thread pipe ring gages...threaded and plain. Threaded ring gages are used to check external pipe screw threaded parts. For taper screw thread pipe ring gages, only one (1) L1 member is required when checking NPT (American National Standard Taper Pipe) threaded parts. Two (2) gage members (GO and NOGO) are required for NPS (American National Standard Straight Pipe) threaded parts.

When gaging NPT threaded parts, thread the marked side on first. Parts being checked are generally acceptable when they come flush to end of ring to plus (+) or minus (-) one turn. The L1 thin ring gage checks the first four (4) threads.

NPTF (Dryseal) and ANPT (Aeronautical) thread tolerances are more closely controlled requiring an L2 thick ring gage as well as the L1 ring. The L2 thick gage checks approximately the fifth (5), sixth (6) and seventh (7) threads.

The plain 6-Step Crest-Check ring gage is used to check the major diameter of the external thread.

Taper pipe ring gages are used in the same manner as pipe plugs except you are now checking an external thread.

EXAMPLE: Thread the pipe ring gage on the part (marked side first). If the part comes flush with end of ring gage, you are at basic thread. Then use the plain ring gage "Basic" steps marked "B" and "BT". If the part comes one (1) turn small from being flush then you are at minimum thread. Then use the plain ring gage "Minimum" steps marked "MN" and "MNT". If the part comes one (1) turn large from being flush then you are at maximum thread. You then use the plain ring gage "Maximum" steps marked "MX" and "MXT".

Again, determine location with your threaded ring (basic, minimum, maximum) before using your plain crest check ring gage.

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