I'm trying to make a gate structure for my attic to prevent people from falling through the pull-down stairs opening. For this, I'm joining threaded iron piping together with elbow joints and t-joints. The problem is that when I try to make a rectangle with four sections of pipe and four elbows/t-joints, I can't attach the fourth corner together because tightening the fourth section of pipe into the fourth joint by turning it clockwise would un-screw the third joint because it would be turning counter-clockwise.

Here is a photo of what I'm doing:

enter image description here

I feel like I'm missing something obvious. And when I googled it, I found this site for building shelves with similar materials and a similar method, but it doesn't mention the problem I'm having.

Could someone please help?

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    Most folks that build the iron pipe type structures for shelves and such do not try to build the pipe into square or rectangle shapes. In the link that you provided if you look closely at the pictures you'll see that the guy has generally not inserted the threaded pipe ends fully into the fittings. So lets say he as used 3 turns of insertion for each joint. To make the last side of the rectangle he would screw in one end of a pipe a total of 6 turns and then go to the last corner and screw the pipe in 3 turns. This makes the other end come back out 3 turns leaving a uniform insertion depth.
    – Michael Karas
    Jun 6, 2016 at 1:14
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    You can also make things out of copper pipe. All the fittings there are slip joint and solder together. Others use PVC pipe for projects like this and that has slip joint fittings that are welded with PVC cement.
    – Michael Karas
    Jun 6, 2016 at 1:16
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    I just saw a closet system on This Old House last week use this method and I had the same question!
    – Evil Elf
    Jun 7, 2016 at 17:52

6 Answers 6


you need a "union" connector. It allows both sides to tighten and then tighten union.

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    google.com/… Jun 6, 2016 at 0:36
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    Unions work great for this application but they do get a bit spendy compared to the other elbows and tees.
    – Michael Karas
    Jun 6, 2016 at 1:19
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    A union is large and maybe ugly compared to a left-hand thread nipple and coupling, which works kinda like a union and will be less obtrusive (however it will be more $$). Jun 6, 2016 at 1:24

If you don't want to have this problem with the last connection, the other option is to use "structural pipe fittings" that clamp onto the pipe instead of using threads. enter image description here


I realize this question is very old. I'm answering anyway, as this is a thing that people commonly want to do!

I'm about to build a water pipe shelving unit that features several closed rectangles. Since this will be a decorative item, I want to use the malleable black iron fittings (like you have), and not the "structural" fittings that appear in one of the other answers.

As you've figured out, you cannot screw together a closed loop made entirely from right-handed threads. To solve this problem, I'm simply going to cheat: I'm going to grind off the threads on one end of one of my pipes. They will be ground down to where I can just press the pipe directly into the fitting without screwing it in. Then, I will screw together all the other fittings, and gently flex the parts to push-fit the final fitting. Finally, I'll make it permanent by tack welding the fitting in an inconspicuous spot.

If you don't want to permanently assemble the parts, you could drill and tap a hole in the junction, and use a set screw to hold the fitting together.

The main challenge is grinding down the threads in a way that still looks good, and not obvious. I have a metal lathe that I will use for this (cheating!), but a more modestly equipped workshop could use a hand drill to rotate the pipe, and an angle grinder, sander, or a file to grind down the threads as the pipe is spinning.

The main challenge would be chucking the pipe into the drill, since it's too large for the chuck to grab it directly. Consider making a jig by buying a threaded end cap that fits over the end of the pipe, and drilling a smaller hole in the center of that cap. Then, you can secure a hex head bolt into the hole using a couple of nuts, and then chuck the bolt head into the drill.

To keep the other end of the pipe from flopping around, you'll want to use something to stabilize it. A cone-shaped mandrel, or a pipe that neatly fits inside the pipe being worked on would work. These could be secured in a bench vise or such. Alternatively, a loose fitting sleeve on the outside of the pipe (such as a coupler or another piece of pipe) would allow you to apply lateral pressure to the pipe so that you could hold the threads against a sander or grinder.


Solution: for the final piece of straight pipe, thread te pipe twice as far up the pipe on one side. Screw the pipe into the 90 to the end. position the final T on the other end and back out the pipe by unscrewing it. Once it touched the opening of the final 90, align the pipe and continue to unscrew the pipe. You will be screwing one joint in as you unscrew the other end. Since you have a deeper thread on on end, stop once the closed loop is sufficiently snug.


Stumbled across this old question. I would say the easiest way is to go to your favorite hardware store's website and type "Galvanized pipe Left & Right" in the search field. No guarantee they'll sell them but my local Home Depot has both nipples and couplings in stock.


Another option (short of welding) would be to use a long piece of solid bar as a joiner, slid inside two pipes on one of the long sides.

You're not very clear about how this thing is supposed to work, so it's hard to say what exactly will work to get you what you want.

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