thread size adapting

[disco_monkey79]

This hovers between the "general" and "metailworking" categories, so apologies to mods if they think it's in the wrong place.

Is there anywhere that sells a good selection of re-thread coil inserts (hope that description makes sense). I'm not 100% sure of the size I'm going from, and the size it needs reducing down to (I suspect the former is 1/2" but I don't know the pitch, and I suspect the latter is M10 x 1.25). I'd really like to visit a shop so I can try out sizes.

Or does anyone know of handy alternate ways of reducing thread sizes, or a cheap-ish tool to accurately measure? I don't want to spend a huge amount on a measuring tool, as this is unlikely to be something I do often. Essentially, I need to screw something on to a threaded shaft, but the shaft is a smaller dia. than the threaded part of the thing that needs to go on.

Thanks!

 

[AndyT]

Not actually an an answer, but if sorting this out means identifying an internal thread that you can't see easily, one method is to trim a bit of wood into a dowel of suitable diameter so that you can turn the metal threaded nut onto it, compressing a thread into the wood. Undo the wood and you then have a visible male thread which you can see to measure and look up in tables. (There are even smartphone apps for measuring external threads.)

 

[Wildman]

for imperial sizes the core dia and tpi would give you a good guide as already said screw in a wooden dowel then unscrew to measure TPI.
Old English machines are usually Whitworth 55 deg threads, American and metric 60 deg threads. So should be easy to identify the thread. ANF and ANC (american threads) are imperial diameters. Metric are obviously metric in dia. A simple vernier will measure core dia. Then look up the details on a thread chart or in a Zeus book.

 

[disco_monkey79]

Thanks all, that dowel idea is ace!

 

[Phil Pascoe]

In case it's a perfectly ordinary thread try to find a bolt that fits, then measure the bolt?

 

[Eric The Viking]

Care to mention what the application is? It's possible people can advise.

For example, American microphone clips and stands are _not_ the same thread as each other. The stand is 5/8" 26tpi (a standard US thread pitch), but mic clips are (supposed to be) 5/8" 27tpi.

5/8-27 is very non-standard, and taps are very hard to find and expensive.

Needless to say, British (European) mic stands and fittings have always used the eminently sensible 3/8" Whitworth. It's also used on professional camera mounting plates, with 1/4" Whit used for consumer cameras and SLRs. You can get thread adapters for all of those, and I even have an odd couple of 5/8-26 to M8 (f2m and vice versa), although I can't imagine ever using them.

The Yanks claim their thread allows you to gently jam the clip on a stand at the desired position (rotation). In practice all it does is strip the threads out of mic clips easily and cross-thread when you're in a hurry.

I hate that 5/8-27 thread so much, all my kit has adapters to male 3/8 Whit Loctited onto the stands, and the reverse adaptors into the mic clips - reliable and robust.

Sorry - rant over.

E.

 

[Myfordman]

Just to correct an impression from the first post.
A thread insert such as a Helicoil is not designed for this task and can only have the same pitch on the male and female threads.
The inside thread will conform to a standard thread and the outside thread will be the same pitch but larger OD and will rarely conform to any standard thread.