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MG Midget and Sprite Technical - Mirror Screws

I'm no good at identifying and procuring things like this screw. The mirror is a Lucas which came with the car, serial 585 - 62046A, but one of the screws was missing. Without it, the mirror gradually droops with the bumps as we drive along (used to drive along).

How can I set about finding the right one?




Nick and Cherry Scoop

You know it has a countersunk head, you can measure the length and width and count the threads per inch (or half inch and double up), with this information you can look at the various sources of tables and descriptions or thread gauges to decide what it is, as an example (only) Willy put up a paper gauge recently (see attached PDF).

To make it easier to count the threads you could use a magnifying glass or take a hi-res photo and zoom in on it having marked whatever fraction of an inch on the screw.

If you have any suitable nuts that have been recorded for their size and type you can try these nuts to confirm thread (fit).

View PDF:
Nigel Atkins

It is probably a BA thread. I cannot get to my car to check unfortunately. Maybe 6BA?

Namrick sell countersunk BA machine screws: https://www.namrick.co.uk/acatalog/B.A.-Screw--Nuts---Washer-Packs.-2BA-Hex.html#a2125

Cheers
Mike
M Wood

The head is a ‘Raised head ‘ slotted- if BA I’d say 2BA (about 5mm)
richard b

Raised, missed typing that bit.

I've lost my BA lists so can't put 'em up.
Nigel Atkins

Nick, is it the same as the two screws that hold the base of the mirror stem to the scuttle? Try it and see. If it is the same as those, then I have some of them to spare and can send you one. They are not chromed though, but polished stainless steel.
GuyW

Thanks very much, everybody. My eyes aren't good enough to count threads, so I took this picture.
I didn't get the threads lined up perfectly with the rule, but it looks like 10 per quarter-inch.
Thanks, Guy. I will go and look.

Nick and Cherry Scoop

No, it's much finer, Guy. One-eighth diameter.
The battery in my digital calipers had died, so I had to get out the micrometer (4" size), calibrate it to the 1" bar, and measure my screw with it.
Actually, I didn't really have to do any of that, but I've got plenty of time at the moment.
Result = 0.125
Nick and Cherry Scoop

This is how they compare.Don't they look horrible when you photograph them?
Thanks for the offer, Guy.

Nick and Cherry Scoop

With a diameter of .125" and 40 TPI, it could be either No. 5 UNC or Whitworth. The difference is in the angle of the thread.
Dave O'Neill 2

Thanks Dave. I hadn't come across Whitworth (to my knowledge), but this morning I tried a screw from my Meccano set (just to see, and it was too big) and now after reading your post and Googling Whitworth, I find that Meccano screws are famously 5/16" Whitworth. Fate.
Nick and Cherry Scoop

Nick – I have found a couple, they measure 0.131 O/D on my calliper, the nut that fits also fits a 4 BA tap. They tell me that’s what it reads. They are countersink round heads. Probably stainless. Seem to be 40 TPI. The Zeus chart only gives the tap drill size: 0.1181. They need to be cut down to half an inch. I can cut them and send them if you like, if they are not suitable no harm done.
L Langley

I am so sorry to be away so long. We are trying to live life in slow motion - taking our pleasures sparingly - and regard all this home time we have as a blessing.
Anyway, L Langley, that was very kind of you. I'm not enough of an engineer to know whether a thix thou thicker thcrew will do the job. I don't think so, but as you say, no harm done.
Nick and Cherry Scoop

Nick - If you e-mail your address on lollipop44@gmx.com
L Langley

Just returning here to sing Lawrence Langley's praises.
He sent a couple of screws, they took ten days to get here, and they fit!!
Thankyouthankyouthankyou.
Nick and Cherry Scoop

nick, I have just restored a Lucas dipping mirror the same as yours. I have used the original stem. It fits ok but is quite close to the screen. Is yours the same??

Bob
Bob Beaumont

This thread was discussed between 12/04/2020 and 06/07/2020

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