NPT vs NPSM thread for conduit nut

[edleit]

This may seem somewhat obvious, but I am trying to confirm whether NPSM (straight mechanical pipe thread) conduit nuts are compatible with NPT (tapered pipe thread) cord grip (i.e., cable gland) bodies.

I have seen posts indicating that the NPSM fittings can be used with NPT fittings as long as a leak-free seal is not required. Since my intention is to provide a locking element for the cable gland, is this a valid application or are locknuts provided with NPT cable gland bodies actually a tapered thread? (seems unlikely given the limited thickness of a nut relative to the taper effect over that length).

Has anyone ever asked themselves this question?

Ed Leitkowski
CT, USA

 

[JohnRBaker]

I've never asked myself that question, but looking back on the times where I've had to install cable glands using those very narrow castellated conduit lock-nuts, I'm not sure that I could've noticed a difference if there was any. In a quick look at vendors for conduit lock-huts (using Google) I couldn't find any notations about tapered versus straight threads. Without some sort of industry standard explicitly stating that this is an issue, it would seem as if the anecdotal evidence indicates that it doesn't matter.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

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[Compositepro]

Lock nuts are straight thread. As you note, what would be the point of a tapered thread here? It could only introduce problems in fit.

 

[BEMPE16524]

don't do it. NPT is tapered. a bit risky especially if you concern about the sealing.

 

[mfgenggear]

Op
My educated guess no. Check the spec for each. Verify major minor diameters. And pd tolerance.
should be on a machinery tool book , machinist handbook.
The go buy male and female, cheap on line. Physically verify
Connection. Be supprized.