What You Should Know About the ANPT 6-Step Plug Gage


ANPT or “Aeronautical National Pipe Taper” Plug Gages are devised for their use on aeronautical components such as plugs, pipes, and other similar fittings that need a thread joint that is sealed mechanically. For these applications, gaskets, O-rings, or straight threads are not applicable. ANPT 6-Step Plug Gage is also used in the same application with its application being different from that of NFTP and NTP plug gages.

The Use of ANPT 6-Step Plug Gage:

The ANPT 6-Step Plug Gage is used for the truncation check of the three-pitch diameter conditions where the plug has a minimum and a maximum truncation step of the pitch diameter conditions. The three conditions include:

  • Minimum
  • Basic, and
  • Maximum

To check truncation, ANPT L1 plug is used in conjunction with ANPT 6-Step Plug Gage. If the face of the product in check lies between the basic minimum and basic maximum steps of the truncation plug, then the L1 plug indicates that the product belongs to the basic pitch diameter.

If the said product falls between the MN and MNT steps, indicates that that product diameter is in the minimum range.

Finally, if the product falls between MX and MXT steps, this indicates that the pitch diameter is maximum.

The three gaging notches of ANPT 6-Step Plug Gage represent tolerance of +/- one turn. The L1 gage is used as a guide that helps in determining the gaging position. The requirements for ANPT 6-Step Plug Gage are spelled out in ANSI SAE AS71051. The ANPT screw threads are designed to have no interface between the crest and the root of the threaded assembly when they are screwed with NPT threads. However, when screwed with NPTF threads, the ANPT thread will have an interference fit between the root and the crest. The fit will either be on the minor or major diameter of the screw thread. This is dependent on the fact which part is NPTF. Finally, to form a seal, sealant will be required because there will be no mechanical seal formed.

Also, it is worth noticing that before the 2-and-a-half-inch marker, the wrenching length of NPT threads and ANTP threads is the same.


WESTport Corporation is your reliable source for quality ANPT 6-Step Plug Gage and other ANPT gages. Established in 1989, WESTport is a manufacturer of quality assurance products that is ISO 6506, ISO 6508, ISO 9001, and ISO/IEC 17025 accredited. With a focus on delivering high quality products at the guaranteed lowest pricescts. WESTport is dedicated to improving product quality and processes to establish its presence as a global leader in quality assurance products and services.

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