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I'm working with 3/4" brass fittings, which seem pretty robust.

Some plumbing fittings should be only finger-tight. My friend said I should use 2 wrenches to make these as tight as I can, and then some.

How tight should I make them?

EDIT: I am plumbing water, but I'd like to learn to plumb gas, too.

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    There is a scientific term: nudge and a grunt tight! – shirlock homes Mar 3 '12 at 11:06
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    Brass threads are softer than other metals, so they seal well. You won't have to get it as tight as steel fittings for example, but you'll want it tighter than hand tight. Is this for gas, or water? – Tester101 Mar 3 '12 at 14:14
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    put a few winds of telfon on the threads and snug them up. Don't go crazy, but use two wrenches and refer to snug and a grunt rule! – shirlock homes Mar 4 '12 at 12:14
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As a general rule, fittings with tapered pipe threads (NPT) should not be assembled to a specific torque because the torque required for a reliable joint varies with thread quality, port and fitting materials, sealant used, and other factors. (Source: Parker Hannifin Catalog 4300 Port End Assembly, page T7)

Leakage path through NPT threads occurs between the very peaks of one thread and the very valley of the opposing thread. No matter how tight you make NPT threads, a leakage path still exists. It is the function of the sealant to block the path between the male and female thread.

This is most helpful!

Most screwed piping is tightened until it feels "right" and the fitting is pointing in the desired direction. What the experienced mechanic is often "feeling" is how the fitting is getting tight. Screw it into until it starts to seat. Then up the force a little by yanking. If each yank gives less movement, you probably have a sound joint. If the movement stops suddenly, you have probably bottomed out. The experienced plumber knows when to stop before he damages the fitting or boss. Caution is advised, tapered pipe fittings into an aluminum boss as excessive torque can crack the boss. This is especially true when using Teflon tape because the low friction of Teflon makes it easy to over-tighten.

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    +1. I believe this is what was meant by "snug and a grunt" -- hand tighten as far as it will go, then wrench tighten just a bit more until it resistance starts to spike upward. – keshlam Dec 2 '14 at 2:50
  • Misleading. NPT (National Pipe Taper) is designed to be sealable without sealant. – Penghe Geng Feb 21 '17 at 22:16
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If using Male and female fitting a seal will be needed eg. teflon tape and firm is sufficent because if you're just jaming the brass together you can break the seal provided by the teflon or similar, if using unions they seal brass to brass and use the above mention nudge and grunt rule, just be carful not to mishape the fitting as brass can crack or bend with undue force.

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    The Teflon tape doesn't create the seal. It reduces friction so you can tighten more with the same turning force. The threads deform each other to make the seal. – Jay Bazuzi Apr 18 '12 at 15:38
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    "just be carful" is not very usful advice: you don't know how much force would be too much until it's too late, right? – Jay Bazuzi Apr 18 '12 at 15:40
  • If Teflon tape doesn't create a seal and is just used for a lubricant as you sugguest why does it come in different thickness? And that would mean that you are using tapered thread brass fitting not parrrell thread, because if you are trying to just bind the threads together they won't only the end of the male fitting touching the inside of the female fitting would and parrrell threads arn't made for that sort of use, unions are. – UNECS Apr 18 '12 at 18:17
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    Just be careful should be applied to reading Wikipedia as well. – UNECS Apr 18 '12 at 18:32
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    @UNECS, I believe the question is asking about tightening tapered threaded fittings, such as NPT and not straight threads. With tapered threads, the threads make the seal as they bind into themselves and sightly deform making a labyrinth seal. The use of teflon tape and or pipe dope will obviously assist in providing a good seal (especially with bad threads) but their use is primarily to provide adequate lubricant. – pdd Oct 19 '12 at 18:03
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There is no specific torque or other fixed installation technique. Use tape dope, tighten to hand tight, 2-3 more turns and leak test the bloody thing.

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According to this reference, the pipe should be in the fitting 9/16" for 3/4 NPT threads.

This one states 0.400 inches for hand tight and 0.5457 for maximum. WRT the above 9/16 is 0.5625 inches, so some minor disagreement there.

This one agrees (within rounding error) with the second (0.400 and 0.546), and also provides a helpful guide for number of turns (4.5 to hand tight, 3 with wrench beyond that)

I also recall, but am not finding a reference for a rule of thumb that there should be 3 threads exposed past the fitting (the picture in the last link is particularly good at showing why, I think, but does not mention the RoT) This sprinkler document does provide something on that line, indicating a range of 3.4-3.9 threads for 1/4 to 1-1/4 pipe sizes, and up to 5.1 on some larger sizes.

And yes, despite any misleading information you may find on the internet, whether it's pipe dope or tape, it is a required "SEALANT" for the helical leak path at the thread roots. Lubrication is all well and good, but that not why it's used. I've personally moved from old-stye dope to teflon tape to new-style teflon dope. YMMV.

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I assume that you are referring to National Pipe Thread fittings. Unfortunately there is no real one answer to the question of how tight should I tighten them as there is may differences between materials and the quality of the threads. This really becomes a "tighten until it just feels right" type of answer and that comes with experience. In general terms you want to aim for 2 to 3 full turns after hand tight. If it still feels loose, complete another full turn. A lot of plumbers will use both teflon tape and pipe dope. Depending on the thickness of the teflon tape you will want to use 3 to 6 wraps in the direction on the threads.

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  • "comes with experience" - Did you do negative testing, where you tighten less than your hypothesis, and get a leak? – Jay Bazuzi Oct 20 '12 at 5:30
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    No, I did not do any negative testing. I was taught this method throughout my apprenticeship. I have had leaks were I was not 100% confident on a joint and you lean from them. When you're plumbing you can't afford to have leaks as they are time consuming to repair. – pdd Oct 22 '12 at 15:25
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PTFE tape DOES seal. NPT threads have a spiral leak path even when fully tight. This is because they engage on the thread flanks, but the roots and crests don't touch each other.

With iron and steel piping, as a general rule, if it doesn't break when you tighten it, it won't ever.

Fittings most often run undersized compared to the standard; in fact, in about half of samples, they are out of tolerance. So it takes fewer turns to reach full tightness.

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Actually, you could just have someone experienced tighten it to the minimum and then have you tighten it another turn or two, that should give you a pretty good idea. That's what I asked my buddy to do for me when I started. 1/2" to 1-1/2" are pretty easy to feel out. The bigger sizes have less of a gradient and that one more turn you think you have might not make it.

Remember, water is the only thing that's really high pressure. After the regulator on the tank gas is like 45psi or lower, like 1/2 to 5 psi in the house. And heating oil is like nill as well unless they have a pump on the tank but then it's still only like 15psi.

Luckily I have never cracked a regulator which is pretty easy to do if you're new, but I did crack an air chuck of my own putting it on a hose. Luckily I had two and it was cheap. I blame the hose maker because the hex bit for the wrench is slighty smaller than the crimp ring making real difficult to grip without screwing up the crimp seal which I have also done. Insert fittings and hose clamps are much better.

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I'd like to suggest that you try the snug and a grunt rule. Use two wrenches so that you will have the right force to insert and still will not deform the fitting.

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    What is this "snug and a grunt rule" you speak of? – Niall C.♦ Oct 18 '12 at 14:07
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Take some old fittings and tighten the till its too tight and breaks or you cant go anymore. Then just back it off a little on the good stuff or use a shorter wrench. It really is one of those things you just have to do to figure out. Break some fittings and you'll understand.

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