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NPT thread gauge stands for National Pipe Tapered Threads gauges. It's a US standard for measuring tapered threads on thread fittings and pipes. Pipes can provide an effective seal for piles utilizing hydraulic fluids. Sometimes referred to MPT, NPT thread gauges are not interchangeable with NPS threads gauges. Unlike straight threads found on a bold a taper thread will pull close, making deeper seal. A sealant compound or PTFE tape has to be used to make sure a leak-free seal.

Characteristics of NPT thread gauge:

  • Angle among taper and the mid axis of pipe is 1° 47’ 24”
  • 60-degree thread angle
  • Truncation of roots and crests are flat
  • Pitch is gauged in threads each inch

Sizing

The taper rate for all NPT thread gauge is 1/16—3/4 in. each foot - which is measured by the alteration of diameter over distance. The outer diameter (OD) of a pipe/fitting must also be measured; both the OD and TPI are needed for perfect identification thread gauge size because more than 1 size can have the same TPI.

Leakage problems associated with NPT thread 

NPT threads gauges were initially made for water piping plumbing, not for hydraulic ecosystems. Though, they've been utilized in hydraulic ecosystems for several years. Pipe threads, in general, are not suggested for top pressure applications as they tend to leak more than any other form of connection. As mentioned earlier, NPT needs some type of sealant placed on the threads before assembly.

These are more likely to leak than their dry seal counterparts, though, either thread sort will leak if under tightened. A usual toughening standard has yet to be established, but remember that tightening needs change with each reuse or type of sealant used. Also, note than, over tightening can crack the female port.

Measuring For A Leak-Free Seal

In this system, TPI is measured by how many threads there's each inch, the metric systems measure the space among 2 threads. Using the trial by error way, try different thread gauges until you determine the closest fit' engage several threads as possible - the more crests engaged, the more correct the reading. Hold the fitting and thread up to the light seeming for gaps among the thread and gauge. This is simpler to see a male link than a female one.

Next measure the diameter with an ID/OD caliper. Male thread diameter is gauged on the OD, another diameter is measured on the ID. Gauges tools recommend holding the caliper at a slight angle for perfect male reading and holding it perpendicular to the thread for more correct female reading.

If the fitting or pipe connection seals on a flared base or inverted angle seat, determine that angle of a seal with seat angle measure on the male connection. Place the thread gauge on the sealing base, if the centerlines of the link and gauge are parallel, the right angle has been determined. 

For a female link, add put the gauge into the connection and place it on the sealing surface. As with the male connector, if the midlines are parallel, the right angles have been determined.