Talk:National pipe thread

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[edit] Tightening

How should NPT threads be tightened? I've heard 2.5 turns beyond hand tight for small fittings, 1.5-2 for larger ones, but I don't have a reference for that. Does anyone have a good source on how to install NPT fittings? Evand 19:21, 8 February 2006 (UTC)

The key standard is ANSI/ASME B1.20.1 "Pipe Threads, General Purpose (Inch)". Table 2 of that reference calls for 3 threads of make-up from hand-tight for pipes 2" and under (nominal), and 2 threads for pipes with nominal sizes over 2 inches. --WaldorfSalad 19:40, 31 July 2006 (UTC)

I do wonder if these recommendations for tightening include items made from copper and brass. Many fittings and valves are so made, and I would never tighten such items to the degree that the above chart suggests. Deformation and splitting could occur. {Jack T., long-time plumber.} —Preceding unsigned comment added by 76.126.182.92 (talk) 13:00, 24 May 2008 (UTC)

[edit] Repeated use

It is my understanding that NPT threads should not be assembled / disassembled repeatedly, since the deformation of the threads causes them to wear out over time. I don't have a reference handy for that. Is this correct? Does anyone have a reference either way? Evand 02:29, 2 August 2006 (UTC)

It depends Evand. NPT seals on the thread flanks without the need to deform. If the thread lube prevents spalling they can be reused many times. NPTF crush on the flats, different situation. By all means add some info on reusability when there is a reference for it. Meggar 07:10, 2 August 2006 (UTC)

[edit] MPT and FPT

It looks like MPT and FPT stand for Male Pipe Thread and Female Pipe Thread, not Male Pipe Taper and Female Pipe Taper. Googling on "Male Pipe Taper" (in quotes) turned up one hit - this article! Googling on "Male Pipe Thread" turned up numerous plumbing sites, including www.septicmaintenanceonline.com/page/8466, which the paragraph in question was plagiarized from. --Javance 18:29, 2 August 2007 (UTC)

[edit] Metric Equivalent?

Is there a metric equivalent? Roger 21:19, 30 October 2007 (UTC)