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No32 Mk3 Thread question.
I am currently getting ready to rebuild several No32 Mk3 scopes, but I am short of some of the 'cap & plug' screws that locate the brass shoes which in turn locate the grat block for the purposes of eliminating backlash. I had assumed they may well be the same as the thread on the screw that fits into the bottom of the clicker plunger housing on Mk1 & Mk2 scopes (1/4" Model Engineer), but it isn't, it's a little larger. At a WAG I think it could be 9/32" ME, although even then there is both a 32 TPI & a 40 TPI version.
It is in effect a screw within a screw, although I don't think the inner thread is too crucial, & I'm sure I can sort that, but the outer screw thread is frustrating me!
I don't have a problem making them, once I have the correct info. I checked the 1971 EMERS for the L1A1 scope, & whilst brief reference is made to the component, the thread is not mentioned. It's pretty nerdy stuff, so I doubt very much it'll be in most texts, although I shall continue looking. Anybody out there know off the top of their head??
I would be eternally grateful for any assistance!
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Last edited by Roger Payne; 05-10-2020 at 03:18 PM.
Reason: typo
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05-10-2020 12:25 PM
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Are you sure that it is not a brass thread size, being as the thread is going into brass? T.P.I. is easy with brass thread because it's all 26 T.P.I.. 1/4" B.S.F. and 1/4" Brass Thread are identical threads, although labeled differently, i.e. a 1/4" B.S.F. tap is identical to a 1/4" Brass Thread tap but labeled differently.
If I have something that is old and British, that is brass with threads in it, I normally consider the possibility of the threads being a Brass Thread and if this is the case I know that the T.P.I. will be 26 T.P.I..
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Thank You to Flying10uk For This Useful Post:
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Roger from memory they were OBA, although 5mm would “fit” it was not a correct “fit”.... will look up in EMERS too, but I’m pretty sure when we made them it was OBA.
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Thank You to DanL96a1 For This Useful Post:
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I would be eternally grateful for any assistance!
I can find nothing specific, but, PL has stated (over the years) that many screws on the MK3 are BA threads.
Mine are not the best, but they are not too bad. I can think of lots of Enfields I'd rather have but instead of constantly striving for more, sometimes it's good to be satisfied with what one has...
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0 B.A. is almost the same as 6 mm x 1mm pitch thread.
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Thank You to Flying10uk For This Useful Post:
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I never thought of 0BA! I want coal cracking over my head! I'm pretty sure I have both taps & die so I'll cautiously try it. I didn't know that 1/4" brass thread was the same as 1/4" BSF Flying 10, many thanks. The thread sizes used on No32's are nearly all BA, mostly 8, & odd ones 10, & even one 12 BA, with the exception of the ME thread used on the MK1 & 2 for the screw that fits into the bottom of the clicker plunger housing. Over the years I've built up a stock of all of these, fortunately.
Many thanks everyone. Much appreciated.
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Bugger! That would have been too easy..........tried a 0 BA plug tap in a couple of Mk3 scope tubes & it is too small by a margin.......just drops in the hole & doesn't even touch the sides (where have I heard that before?). If Daniel's is definitely 0 BA that raises a question; were there different sizes used, were some modified?? Any road up my holes are bigger than 0 BA!?! I bit the bullet & ordered two carbon steel 9/32" ME dies (one 32 TPI & one 40 TPI - my money's on the 40 TPI) from Tracey tools. They're only three quid each & carbon steel will be perfectly good enough for brass.........if they fit! We'll see.
Thanks for the suggestions offered so far anyway.
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Would the bigger holes be from a rebuild.
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Yes, that's a point.....I suppose it could be.......thread stripped so open it out to the next size up. Out of interest I'll try checking the threads on another couple of scopes when I get a minute.
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In my box of bits I have a tap marked 1/8 GAS, this looks to have 32tpi and I think it is the same as 1/8 ins bsp. This is bigger than 1/4 in and approx 5/16 in.
Could this be the thread? Undeniably British and usually used on brass gas fittings.
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