I don't know if anyone can help me, as far as I've found out, the threads on Doherty choke and advance levers (Norton's) is a thread called 10-28 tpi UNS. I need a couple a bit longer than normal, just under an inch long. I can't find anywhere that sells these. I have seen taps and dies for sale in this size so could get one made. Even the screw size is odd at 0.190", so not 3/16ths or any of the usual sizes. Can anyone help please?

email (option): horror@blueyonder.co.uk

1BA? Ron

https://stainlessmiddleton.co.uk/45-cheese

email (option): ronpier@talk21.com

Thanks Ron, is that the size it is? I couldn't find out any screw diameters for BA sizes.

email (option): horror@blueyonder.co.uk

Dave lots of these levers use 1BA screws, the size given is .2090"diam x 28.22 tpi. If you can't find those 10-28's?? then a run through with a 1BA tap might sort it. Ron

email (option): ronpier@talk21.com

Yes that is a bit bigger so it's an option, thanks

email (option): horror@blueyonder.co.uk

'UNS' is 'Unified Non-Standard' so it's an American thread and not likely to be found on British motorcycle controls.

I suspect that it is another non-standard cycle thread - a rare version of 3/16" which has a .1875 diameter so very close to what you have measured.

The WD spare parts lists don't show thread details for the lever screws but they do on the twistgrips.


how to delete an ebay account


A 1 BA tap will go most of the way but will tighten up before it clears these threads...not ideal if you have a nice new thread. If anyone has a 3/16" x 26 tpi cycle die then I'd suspect it would be Jan.

'UNS' is Unified Special...Ian

email (option): ian@wright52.plus.com

It's definitely 28tpi not 26 cycle thread. I have a 3/16 X 26 tap but it's too big. Yes I can change the thread but I only want to fit a longer screw on 1 of each of the lever holes to go on a combination set, so that would mean 1 original and 1 screw of a different size. Not ideal. 2BA is a bit small but loosely screws into the hole. I've never heard of 10-28tpi UNS but it fitted the size I've got when I googles the diameter and tpi. I've also got another set of levers that has a metric size screwed in that fits very well. Again, not ideal but it's a lot closer size.

email (option): horror@blueyonder.co.uk

Text me your address if you need to borrow a 1BA tap to try. Ron

email (option): ronpier@talk21.com

I wrote 3/6" x 26tpi in error. As per the Spare Parts List, they are indeed 28tpi...Original screw thread on small wartime-produced parts was not always that high...

Thanks, I'll be at yours in a couple of weeks Ron so I'll get it then. I've got lots to be getting on with in the mean time.
I don't want to ruin good original parts if I can help it so I'll try and get a tap and die in the correct size if possible. It looks like 3/16x28 is a UNS size the same as 10-28tpi I mentioned earlier.

https://www.tracytools.com/3-16-x-28-tpi unfortunately this place is out of stock. I'll try Uni-thread who I usually use but they don't have anything listed.

email (option): horror@blueyonder.co.uk

Paul at Uni-thread is a very helpful chap, after lots of guessing and confusion trying to find a thread that's 0.196" X 28 and with the throttle screws being 3/16 X 28 but too big for the choke mount, I sent the screw to Paul. They enlarge it onto a screen so it can be measures more accurately, the screw was worn so smaller than it should be and guess what...! The ginger oracle was correct, it's 1BA, well done Ron :slightly_smiling_face:
So not the same as the throttle. The good news is it's easy to get some screws. I should have just phoned you Ron and asked in the first place :thinking_face:

email (option): horror@blueyonder.co.uk

I've booked a table at our local Harvester for next week....Mine's a whiskey!! Ron

email (option): ronpier@talk21.com

A whiskey or 2 as usual then Ron :tropical_drink: :grinning:

email (option): horror@blueyonder.co.uk

Gents,

An old post but I want to add to it anyway.

The screws to fit the Doherty square edged air and ignition control lever housings on an early Norton are definitly 3/16 x 28 tpi, they are not UNS 10-28 and also not 1 BA.
I had to make them and used an old fashioned die wrench with loose 1/4 x 28 tpi UNF cutting plates. Brought dia to 4,8 mm and cut the thread with that.
They fit perfectly into the control housings, as well as in the throttle control clips.
Thread angle is identical to the single original screw I had, checked by fitting the threads together (eyeball Mk 1 observation).

Likely a Doherty attempt to assure delivery of spare parts by using proprietary screws.

Other brand levers may well have been 1 BA, I doubt 10-28 UNS was ever used in the British industry of the time.
The UN definitions came when threads were universally specified in 1949.

Cheers,

Rob

email (option): wd16h@telfort.nl

email (option): wd.register@gmail.com