Working Out A Thread

What the thread is part of may help to give a clue, such as country of origin etc.

Age also helps, as very early things would have been different to the metric threads which are common now.

There is a thread comparison chart on our website which gives nearly all the popular 'old fashioned' threads plus Metric. There are 4 pages:

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

I prefer a piece of dowel on a small hole. It won't stretch like blu-tack and can be safely screwed out, leaving good thread marks on the wood.

-adrian

With much larger threads (Triumph motorbike clutch hub) I used plastic padding glopped onto a piece of perforated zinc. A bit of oil on the threads makes a good release agent and the bodge shrinks fractionally when it sets as well. In this case, I might use the same technique, but stick a small screwdriver into the bodge until it had set, then unscrew it.

Obviously, Michael needs to get an idea of the OD of the thread,

Mark Rand RTFM

Hi Michael,

Being slightly mischevous I thought I would hand you this link to one of Tony Griffiths' web pages

discovered it the other day and was amazed how many different thread types have been invented over the years.

Fortunately it normally boils down to a small subset, with age and country of origin being good clues, as are type of material it is going into, and application (e.g. BA used to be popular for electrical fittings). Of course if its part of a larger bit of kit, then find out what the rest of the threads are (especially if the problem one is mangled).

If you find the ID of the hole then you have an estimate of the tapping drill size, then you can look through a link like this one

to identify the most likely candidates. You can then elminiate by trying known threaded screws in the hole, and see what is left.

Steve in Cheshire

Here's a different table of thread dimensions that may help:

Guy

Yes - this will give a fairly accurate measure of pitch, which is half the battle.

BugBear

Thanks guys,

I'll find a suitable piece and stick it in and see what comes up.

It's for 1) an American motor*, there are four mounting holes on the face of it, and 2) an old pneumatic ram that's currently on its way to me.

*Jim (Pentagrid), don't know if your still on here, but it's one of the Leeson motors I picked up off you.

Cheers,

Michael

Two-part silicone doesn't shrink significantly, also you can slice it with a scalpel blade and measure thread angle and tip and root profiles on a profile projector, if you have access to one.

Leeson still make motors. If it has a plate on it you could e-mail them, but from what I can see on their website the smaller frames have

4 holes 1/4" UNC (thats 20tpi) set at 3 3/4" diameter. That will give a hole of 5mm ID.

Steve in Cheshire