1/4" x 32 UNEF

[steelfixer]

Seeing they are both Russian there is a fair chance you might be right Andy.

[Peter Drew]

This thread (pun intended) has got longer legs than I expected, The UN in UNEF might as well stand for UNusual . I've just had another look at my Tento, it's possible to tap the existing thread out to 1/4 Whit or UNC to a depth of 12mm. The eventual L bracket will need packing out a bit to clear the prism housings.

[cloudythoughts]

If you want to test the thread it is the same as an old toggle switch.

It must be an old old one though as the new ones are metric.

If you rearly get stuck you can soon make one as the dies are readily available.

If this is not possible for you to do let me know and I will make one for you.

Very useful info. I have a few vey old bits and bobs in a box someplace.. Do you mean a mains toggle switch or automotive?

I'm holding my head close to my pc monitor, so you have easy access to slap me through the screen.....

It wouldn't be M6 fine(M6 x 0.75, compared with the std/coarse M6 x 1.00) would it??

Basically a metric version of the UNEF? Converted to TPI, it would be 33.87.

My Russian Tal 200K has six primary collimation setscrews that use this size.

If that's it you'll all need to slap me. Never knew there was an M6 fine. I guess the M6 I tried was M6 standard. If it is M6 fine then my measurement of 33.9 TPI would be bang on!

This thread (pun intended) has got longer legs than I expected, The UN in UNEF might as well stand for UNusual . I've just had another look at my Tento, it's possible to tap the existing thread out to 1/4 Whit or UNC to a depth of 12mm. The eventual L bracket will need packing out a bit to clear the prism housings.

Me too. I though it was such a simple question at the start.

Now also looking for an M6 Fine to tryout that theory.