Odd Screw Threads (can anyone help?)

[Tim Bayliss]

Hello all,
I have a small project on the go that entails matching the screw threads on a proprietry piece of equipment. I have measured the threads and have found them to be really odd. The threads are very worn so I can't judge the thread angle but the O/D's & pitches, as well as I can tell, are -

thread 1 - 0.145"O/D x 36 TPI (maybe 3.7mm x 0.7p?)
thread 2 - 0.200"O/D x 25 TPI (M5 x 1.0p is a reasonable fit for this one).

I have looked at all the screw thread tables I have but can't find these anywhere.
I am guessing that they are imperial threads because the equipment was made in England some time ago, but one never knows! They could well be the manufacturers special proprietry threads.
If anyone has come across these or can tell me where I could get taps & dies I will be grateful.
Thanks in anticipation,
Tim

[Roger Mason]

Hi,

Tim asked about odd threads.

Have you looked at American threads? My book suggests: 7-36 is 0.151" O/Dia and 36 t.p.i. However I am not sure if this is a popular size - I have only come across even numbers in this series. The other thread could be 12-24 which has a 0.216" O/Dia.

I hope this helps.

Cheers,


Roger Mason, in St. Agnes.

[jackrae]

For both taps and dies at very reasonable prices you could try Tracy Tools of 2 Mayors Avenue Dartmouth Devon TQ6 9NF Telephone No is 01803 833134

They're most helpful and their free catalogue is a wealth of shapes and sizes

Give them a call, they might fix you up over the phone

If the item is British and it's old (greater than 50 years) then it is very unlikely that it is a metric thread.

Jack

[Tim Bayliss]

Thanks for the response lads,
You are probably correct Roger, the smaller of the two threads may well be 7-36 UNF but taps & dies aren't available, I've tried a couple of tap manufacturers & they can only offer specially made ones at a great cost. I may try a sloppy 4BA as a 'jam' fit.
As for the larger one, I'll probably get away with M5x1p., it's close enough for my purposes.
Tracy Tools were, as always, very helpful but didn't recognise these threads.
While I was searching the net I did find an outstanding and comprehensive list of screw thread sizes on a private web page, www.adneish.freeserve.co.uk. It's a stunning and very useful piece of tabulation and must have taken ages to compile, have a look.
Regards,
Tim

[Phil Sutton]

Hi Tim,it's apity you don't know anyone in the states or who is going there for a holiday,who could pick a few up for you.It may be possable to buy them over the net,as an alternative.

Phil