Amal carb - new. Throttle stop screw size

[Craigy]

Hi folks,
I have a new Amal carb (276?) on my 1952 A10 which is missing the throttle stop screw. Are the new carbs thread metric?

A friend gave me an old screw but it only goes in a few turns.

Sorry I can’t attach pics as file it too large.

Any help on size/thread would be helpful.

Cheers

[morris]

By the look of it I'd say it's 1/4 BSW? There seems to be only one size for all types.
https://amalcarb.co.uk/throttle-stop-screw-washer.html

[Rex]

I've only ever seen Whit on those carbs (mainly Velo) which have a slide-lifting screw here. Whit would be too coarse for a regular throttle stop screw.
Never looked into it, but I'd assume they're BA.

[Triton Thrasher]

By the look of it I'd say it's 1/4 BSW? There seems to be only one size for all types.
https://amalcarb.co.uk/throttle-stop-screw-washer.html

That’s a screw for a Concentric.

Looks like neither 1/4”, nor BSW.

[JulianS]

Ask Amal? I have found them very helpful.

https://amalcarb.co.uk/contact

[trevinoz]

I think 1BA on the 276. 2BA on Monobloc. Modern make could be anything.

[Slymo]

Quite likely BA which is a metric pitch.

[Craigy]

The tread turned out to be BA1

[Triton Thrasher]

Quite likely BA which is a metric pitch.

It’s only “sort of” metric!

[Craigy]

‘Nearly metric’? 🤣

[groily]

https://www.sizes.com/library/technology/thread_BA1.htm explains all.
Starts at M6 (0BA) and each successive smaller size has a pitch that's 90% of the one larger, rounded as necessary when the decimal points get silly. So 1BA is 0.9mm pitch, 2BA 0.81mm, etc etc down to 25BA with a major diameter of 0.25mm or 10 thou . . .
Odd sizes were not generally recommended for widespread use  - but folk like Lucas used a lot of 3 and 5 along with 2, 4 and 6. Smaller than 6 probably never seen in the world of our toys (unless inside chronometrics maybe?).
For sizes & specs, see https://web.archive.org/web/20051105165558/http://shopswarf.orcon.net.nz/ba.html
Screws and nuts available from multiple sources - I favour https://www.ba-bolts.co.uk/ for them, and the ever-present Tracy Tools for tackle to make them: https://www.tracytools.com/product-category/taps-and-dies/ba-taps-dies/ and https://www.tracytools.com/product-category/helicoil-thread-repair-kits/thread-repair-kit-ba/ (5BA inserts not available from them.) Hex bar is available in some AF sizes, or close.