Paralell and straight threads

[JayJay1978]

I bought some 1/2" x 15mm adaptors today from the a plumbers merchants, you know the ones they have a 1/2" BSP male thread (male iron?) and a 15mm comp fitting.

Upon getting them home I noticed they were both different, one has a slightly shorter straight BSP thread with a small 'flange' on the hex flats.

The other had no flange and a longer slightly tapered thread.

Its obvious due to their similar apperance that they've been mixed up but is the tapered thread a gas fitting? I've read somewhere that straight thread are difficult to seal, whats that all about?

 

[doitall]

Parallel threads can be used for virtually anything, whereas taper threads are better for iron, making boilers up etc.

Parallel threads should always be used with brass and aly fittings, like gas valve etc.

Get yourself a roll of Loctite 55 string, you wont regret it, but keep the lid on it, when not in use as it does dry out.

 

[JayJay1978]

Cheers doitall.

 

[bengasman]

Depending on if you want to use them all for the same thing or not, it might be an idea to swap the ones that are "wrong" for the purpose.

Personally, I only use parallel threads for those connections that can be sealed with a washer, everything else I prefer taper. The problem with sealing parallel threads with tape, is that it does not have much resistance against loosening up, unless you manage to get the thread in all the way to where it runs out.

 

[doitall]

Loctite 55 Ben

 

[bengasman]

How well does it hold under mechanical (rotational) forces?

 

[doitall]

How well does it hold under mechanical (rotational) forces?

An example please.

I've used it on 2" gas pipe, and a 4" water main at 4bar, it's as good as boss white and hemp, but a lot more expensive, but it is ok to use with potable water.

 

[bengasman]

What I meant was: how good is it at keeping it from getting undone if both male and female are parallel?
I'm not that worried about leaks, both string and (gas)tape will do the job. But as teflon has the world record for low friction, it does not do a lot for holding things in place.

 

[kirkgas]

I bought some 1/2" x 15mm adaptors today from the a plumbers merchants, you know the ones they have a 1/2" BSP male thread (male iron?) and a 15mm comp fitting.

Upon getting them home I noticed they were both different, one has a slightly shorter straight BSP thread with a small 'flange' on the hex flats.

The other had no flange and a longer slightly tapered thread.

Its obvious due to their similar apperance that they've been mixed up but is the tapered thread a gas fitting? I've read somewhere that straight thread are difficult to seal, whats that all about?

one sounds like the correct fitting, and the one without the flange sounds like a straight coupling with a nut and ring missing

 

[doitall]

What I meant was: how good is it at keeping it from getting undone if both male and female are parallel?
I'm not that worried about leaks, both string and (gas)tape will do the job. But as teflon has the world record for low friction, it does not do a lot for holding things in place.

Try and unscrew a 2"steel pipe that's been made up with it.

Good practice would say you rough up the threads on brass and chrome fittings, whatever sealing material is used.

It is good and I would recommend it to anyone, the only stipulation is, that you must keep the lid on the pot to avoid it drying out.