by Jerry
(Paramus, NJ)
What is the difference between a 1/4 NPT and an 1/4 NPT I/M fitting?
Are they inter changeable?
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Hi Jerry…
I do not recognize the I/M portion of the thread name. NPT is, of course, national pipe taper.
Knowing where you found the name might help.
I could guess that I/M might stand for imperial / metric, which would suggest that it is a thread designed to be used in both imperial and metric ports.
When you measure the O.D. of the thread, is it the same for both?
![Guide to NPT fitting size](https://www.about-air-compressors.com/wp-content/uploads/2019/02/NPT-chart.gif)
If so, then the next step is to thread both into a 1/4 port and see how many threads penetrate before they cannot be threaded further. If they penetrate 4+ threads, then that would suggest that they are useful in both metric and imperial port sizes.
Anyone else from the wider pneumatic community an offer advice here?
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I/M couplers
NPT is NPT, and refers to the threaded end.
“I/M style” (apparently) refers to “Industrial / Milton”, meaning the garden variety of couplers that usually come with DIY compressors.
The bump near the tip of the male I/M connector is narrow, about a 16th inch at the outside diameter.
The bump on a “T” connector (Tru-Flate) is mostly used in automotive shops, and has about an 8th inch wide flat at the end.
There are “I/M”, “T” and ‘universal’ “U” female checked couplers. The “U” connectors work with either “I/M” or “T” males, but are not truely universal.
All are commonly sold at big-box stores.
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