Why are these brass connectors binding up?

Having trouble with brass pipe connectors.

I have a M+F pair of connectors I want to use to make a ~air tight connection through a thick piece of rubber.  Want to screw the parts together far enough that the hex-nut section of each part will act as a flange, and crimp the rubber in between.

However, I can not get the parts to thread together far enough.  At about 1/2 the length of either, the connectors start binding up.  I can only get the two about 1/4" away from being fully seated.


Are pipe connectors manufactured with a slight taper to create this? Or something else?

Any suggestions?

Picture of Why are these brass connectors binding up?
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These are Tapered threads !! The whole idea is they seal VERY VERY well, as you drive them together.

To do what you want to do, you need a parallel thread in the male part.

bwrussell5 years ago
Pipe fittings are tapered. If you get a lubricant, graphite powder might work, you can probably get a little more out of them but the easiest solution would be to get a couple of washers. Place one on each side of the rubber and the flanges will provide the clamping force. A little Teflon tape will guarantee an air tight seal.
Not ALL pipe fittings are tapered. You can readily buy "NPT" or "NPP" fittings in the US, or BSP and BSPT in quite a lot of the rest of the world.

Of course but the standard for pipe threads is tapered, NPT or BSP (Which is the same thing as BSPT, the t stands for thread. The British pipe standard for straight threads is BSPP, for parallel. BSPF and BSPM were also used).

Also I don't think NPP is a thing, at least for pipe threads, can't find anything on google or McMaster-Carr and have never dealt with a thread called that professionally. There are NPSC, NPSM, and NPSL for straight pipe threads in the US standard. You can also typically get smaller fittings in UNC/F standard threads.
No, certainly not in our parlance. BSPT is T for tapered. Otherwise BSP is parallel. Certainly, in common practice where I am in the UK, we refer to your pipe threads as "NPT" and "NPP" when designed in, to make sure you make the right parts.... There is the same misunderstanding about what the T means on your parts, as you are making with ours......

CTS-Chris5 years ago
hi, an idea here I've used.if you want to ream the threads all the way flush from a bevel or even damaged threads use this technique.

get a nut sized to your need same size as the tread you want to cut.
use steel nut and saw notches with a hacksaw halfway into the face of the nut.
use sand paper to smooth the bevel off of the side you cut into giving you a flush surface. (should be halfway into the 1st thread ,the more cuts the easier the job)
use it like a Thread Cutting Die.
Unlike a Thread Cutting Die which tapers and has has tapered teeth a nut cut in this way will allow you to run threads farther up your fittings (almost flush) in a consistent manner.
if i get some request ill make an Ible showing the process
canucksgirl5 years ago
I looked at your image at full size, and it doesn't look like its tapered, but at least one part (the female end connected to the male), looks like its been banged up a bit. The threads have some tiny nicks/burrs and if the other parts do too, they might be causing the binding. You can test this by running a cotton ball over the threads. If there are any burrs, the cotton will catch on them, and then you'll know.

I have also had problems in the past with these kind of fittings (I use to work in a Truck and Trailer Parts Dept.), and they can sometimes be a little finicky for no reason. So, I would suggest trying some WD-40 (a lubricant) on your connections to see if that makes them thread a little easier; or you could use some teflon pipe tape.