No32 Mk3 Thread question.

[Roger Payne]

Many thanks Bill, but it's a little smaller than 5/16". I've dropped a micrometer across several original examples now, & apart from one that looks to have crushed threads & which measures about .285, all of the other three or four are consistent to within a thou at .295/.296" (diameter measured across the top of the threads). My 9/32" ME dies arrived today & it doesn't appear to be either of those. It's quite a fine thread. I'm stumped at the moment.

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[Scout Sniper]

Have you tried, 9/32 BSF (British Standard Fine)

[Roger Payne]

I'd only got the die pinched up (without realising it) when I tried the 9/32 ME x 40 TPI earlier. I've just tried it again & the fit is ok. I can now get a few spare parts made & in due course one or two Mk3 scopes assembled.

It's been driving me nuts for the last few days....!

[Scout Sniper]

The smile says it all!! Well done mate, always nice to find that elusive thread!

I am currently restoring a model steam engine and boiler and its been made using any tap and die they could find i reckon, as there is no continuity whatsoever in the threads used!!

[Roger Payne]

Thanks. I understand your predicament entirely!

[30Three]

Great to get a result. Look forward to seeing those scopes when their finished. keep us updated!

[Flying10uk]

A chap that I use to know, sadly no-longer with us, used a method of ascertaining the T.P.I. of larger internal threads by applying a little oil to the thread in question. He then pressed a piece of paper against the thread and when the paper was withdrawn the "crests" of the threads were left imprinted on the paper which he then counted and figured out the T.P.I.. It's not really practical with a thread as small as 9/32" but it's a tip worth remembering and it was fascinating watching the chap figure out the T.P.I. of a thread using this method.

[Roger Payne]

Thanks, I'm always open to any suggestions or advice to make life easier. I'll file that away ready to use next time I have such a problem!

[Surpmil]

I take that is a safety plug in the end of the tube to guard against falls? A wise policy!

[Roger Payne]

Actually, I intend to spin the tube in my Myford as I have a few scopes, including at least one Mk3 where the ocular end is torn, corroded away or otherwise severely damaged & will need replacing by grafting a No42 or 53 ocular end in place. That plug is a fairly tight fit into objective end of the scope tube, & I have turned another one for the ocular end (complete with cone) so I can spin the tube about centres to turn off the damaged ocular end & step the tube so I can then silver solder the new replacement end in place.

But you make an excellent point. Before now I have dolleyed out a nasty dent only to drop the scope tube & put it back in! I now tend to use redundant No42 ocular lens retaining rings when I have a scope stripped down, as this does offer some protection from bumps, the retaining ring taking the knock rather than the end of the tube itself.