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How tight do you have to tighten National Pipe Thread?

They should be hand tightened and then another 1 or 2 turns, but no more. More turns will put to much pressure on the fitting and may crack it and cause a leak. The Tensile Stress created by tightening the fitting beyond hand tight and 1 or 2 more turns will crack the female fittings.

A sealant should be used that is compatible with the material of the fittings. Teflon paste, pipe dope, and too much Teflon tape should not be used as this creates bulk which will create more stress and may lubricate fittings causing you to over tighten them. If Teflon tape is used it should not be more then 2.5 mil thick and care should be taken not to over tighten threaded joints.


The smaller the pipe size the easier it is to crack it. It is easy to over-torque smaller diameter fittings because their resistance to torque is less.


Title: How tight do you have to tighten National Pipe Thread?
Description: Information on tightening NPT fittings
Published: 1/29/2008
Last Edited: 10/3/2013
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