Taper/parrallel thread - what is the difference?

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Amari

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Re recent post concerning whether to put plumbers' tape on a skin fitting, advice from forumites seemed to depend on whether thread was taper or parallalel. What is the difference and how d'you tell, please /forums/images/graemlins/confused.gif
 
Tapered threads are errr......... tapered.

BSP are tapered threads but there is BSPP parallel thread as well. A tapered thread tightens naturally wheras a parallel thread doesn't.

PS the taper is normally quite apparent the thread will be visibly smaller at the end of a male fitting.
 
Quite a lot, actually!

Yer average machine screw/bolt is parallel thread - that is, all the theads are the same diameter, no matter how ling the threaded bit is.

A tapered thread implies that the threads nearest the end are a smaller diameter than the others, as is applied to a cone.

Having said that, the only place I can remember encountering a tapered thread is on the end of a mop-handle (apart from the tubes on a drilling rig - and that doesn't really count in this case). I have never seen a plumbing fitting that didn't have a parallel thread. I stand (sit) prepared to be proved wrong.

Edit: I must learn to type faster. I've still never seen a pipe fitting with a tapered thread.
 
They are regularly used on engines as anode holders.

PTFE tape should not be used IMHO in case it interferes with the electrical contact.

Also used on old rad valves where PTFE tape should be used.
 
You can tell a tapper as you tighten it gets harder and squeaks.
The idea is a water tight seal is made as the threads are forced closed.
 
Have noticed to my cost, some spark plugs on cars have a tapered thread.

This means that no lubricant can't get down the plughole.

Me, and also the garage on one occasion managed to break the plugs which resulted in the head coming off and helicoils etc. Expensive.

Motto - change plugs regularly.
 
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BSP are tapered threads but there is BSPP parallel thread as well.

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There is also BSPT, to specify tapered. We use a lot of Ball valves, and always specify the thread type, to avoid confusion of just saying BSP.
 
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Have noticed to my cost, some spark plugs on cars have a tapered thread.

This means that no lubricant can't get down the plughole.

Me, and also the garage on one occasion managed to break the plugs which resulted in the head coming off and helicoils etc. Expensive.

Motto - change plugs regularly.

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Spark plugs with conical threads, repaired by a Helicoil?

Surely some mistake!

I have yet to see a tapered spark plug thead, nor a helicoil thus shaped...
 
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Have noticed to my cost, some spark plugs on cars have a tapered thread.

This means that no lubricant can't get down the plughole.

Me, and also the garage on one occasion managed to break the plugs which resulted in the head coming off and helicoils etc. Expensive.

Motto - change plugs regularly.

[/ QUOTE ]

Spark plugs with conical threads, repaired by a Helicoil?

Surely some mistake!

I have yet to see a tapered spark plug thead, nor a helicoil thus shaped...

[/ QUOTE ]

I seem to recall that the B.L.1.6 and maybe 2.0 engines used in Montegos and Maestros used taper thread plugs. One was warned not to tighten them too much. They sealed without the aid of a washer.
 
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I seem to recall that the B.L.1.6 and maybe 2.0 engines used in Montegos and Maestros used taper thread plugs. One was warned not to tighten them too much. They sealed without the aid of a washer.

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...mmm ...checked my old MG Maestro plugs 1.6 R series engine.... parallel thread !
 
I have never seen or heard of a taper thread on a spark plug, many plugs have conical seats that seal without a washer. Most plugs break because they are not removed at least once a year, Fiesta 1100 are most common.
 
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Have noticed to my cost, some spark plugs on cars have a tapered thread.



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I don't remember any tapered thread spark plugs (there could be loads) but I do recall some plugs with out washers had tapered shoulders. The actual thread was parallel.

Princess 2000 circa 1979 ?????????????

Yamaha RD350 YPVS ???????????????

Mariner 55 ?????????????
 
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I have never seen or heard of a taper thread on a spark plug, many plugs have conical seats that seal without a washer. Most plugs break because they are not removed at least once a year, Fiesta 1100 are most common.

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Yes. Think I have got it wrong again. Fiesta/KA engine is what I'am talking about.

Sure the engineer said tapered but now obviously conical. Thanks for the knowledge.

I know what to do.......................
 
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