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View Full Version : NPT thread length to tighten

Lakee911
10-12-2009, 06:34 PM
I need to get some 3/4 pipe cut and threaded. On average, how much threads in to the coupling?

Peter Griffin
10-12-2009, 06:37 PM
There should be 7 perfect threads and 3 to 4 imperfect threads. tighten 3 turns by hand and 3 by wrench.

Lakee911
10-12-2009, 06:45 PM
Sorry .... I should have been more specific ...

From fitting to fitting let's say I need 18" ... how long should the pipe be? In other words, how much (in length) threads in?

Peter Griffin
10-12-2009, 06:57 PM
Ah, 3/8 + 3/8 or 3/4"

Winslow
10-12-2009, 09:54 PM
Sorry .... I should have been more specific ...

From fitting to fitting let's say I need 18" ... how long should the pipe be? In other words, how much (in length) threads in?

measure from center to center then deduct 3/4 inch per fitting (11/2 inches total).

jimbo
10-13-2009, 06:44 AM
3/4 per fitting is probably closer to accurate. But you have to remember that this is never an exact science. Threads vary, depending on who cut it , how the dies were set on the machine, etc. Factory threads on a piece of pipe will often be different that field cut threads. Adding up a fitting on each end of a pipe, there could easily be 2 to 4 turns total difference in "tight". The experience gained over time ( we call it wisdom, others call it learning from your mistakes!) helps to make these things work out.

hj
10-13-2009, 06:58 AM
The setting of the die, the way the fitting was tapped, the size of the pipe wrench, and YOUR build will all conspire to determine the answer to your question. It is NOT an exact science so you have to use some discretion in your measurements.

Lakee911
10-13-2009, 04:43 PM
Thanks. :)