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MG Midget and Sprite Technical - What size thread are the rev light screws?

I've got to make up a new captive nut for the screws that hold the reverse light in place. Anyone know what size they are? I've measured one up and I can't work it out. Looks like 0.132" x 32 TPI Definitely bigger than 1/8". Part no. 27H8811.
Greg H

Greg, I think they may be 4BA which is 0.142 and 38.5 TPI but I haven't actually checked them to be sure.
M McAndrew

Greg,

Mine being a Heritage shell did not have captive nuts - set screw goes right through and nut/washer on inside.

Thread may well be 2 BA as similar to 32tpi.

R.
richard boobier

On checking the car I think I used 4BA as advised above.

R.
richard boobier

0.132" x 32 TPI is a 6-32 American machine screw thread. Cheers - Dave
David DuBois

Good suggestions but they're not 4 or 2BA. 4BA is a finer thread. 2BA is larger OD. 4BA in pic.

David 6-32 sounds about right but is that just American or a thread that was also used in England?

I could put a different size screw in if I really have to.

Greg H

Greg - 6-32 is an American machine screw (course thread). To my knowledge there is no equivalent British screw of the same size and thread (or even thread form). I could send you some if you need them. Cheers - Dave
David DuBois

Thanks for the offer but I should be able to find some if that's what it is. Although I'm a little sceptical that an American thread would be hiding on my English car.
Greg H

have you tried 3/16" unc /
HALL JOHN

Greg - "Although I'm a little sceptical that an American thread would be hiding on my English car."

All MGs coming out between 62 - 80 used American threads, with very few exceptions, so it would not be surprising to fine a 6-32 lurking about (although most machine screws used were 10-32). Cheers - Dave
David DuBois

My listing shows it as No 6 UNC, which is 32 tpi
Paul Walbran

Gentlemen. During the Second World War, the British and US forces used many of each others equipments. US aircraft were supplied to the UK but the tools needed to work on them, and the nuts and bolts, were of different patterns. In a similar vein, the Rolls-Royce Merlin engine was supplied to the US for use in some of its fighter aircraft--again requiring different tools and different nuts and bolts.

About 1947, the UK, Canada, and the US decided that, should they ever be in a similar situation again, it would be useful if all three nations had basic machine products using the same thread forms and capable of being worked on without the need for special tools. At that time, it was decided that wrenches, rather than being marked for the size of the bolt they were to fit--e.g. 1/2 W, would be marked with the size of the bolt head they would fit. This was measured "across the flats" and is noted as AF. In a similar move, sizes of the various bolts, screws, and nuts were standardized along with the thread form (i.e. 60 degree) and that two basic thread forms, fine and coarse, would be made for each size of bolt/screw/nut. This was called the "Unified National System" and the various products are marked UNC, for Unified National Coarse, or UNF, for Unified National Fine.

Thus, these parts are not "American", but rather the result of the Unified system which the three nations developed jointly to meet their perceived security needs. It is quite common to find Unified parts in use in MGs, especially the later ones as the earlier systems became obsolete and the new standard was incorporated.

Les
Les Bengtson

Thanks Les nice clear explanation
Nigel Atkins

Well sounds like 6-32 then.

Thanks for the nice bit of trivia. I had wondered about the origins of the imperial bolts. A very rational thing to do but some of us didn't standardise on the terminology of the tools. I don't have any wrenches but I have plenty of spanners and they seem to work well enough. lol
Greg H

thanks Greg - you've just made a Pom spill his tea and roar with laughter! Wrenches indeed....
David Smith

This thread was discussed between 27/11/2011 and 29/11/2011

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