Gary

Here's the conversion chart I have developed to convert BA to UNC/UNF threads which I have used on my projects. I normally make all my hex headed screws and nuts from hex stock. If you want I can email you a PDF of the chart if you PM me your e-mail address.

John

Edited By John Purdy on 05/05/2022 17:41:39

Edited By John Purdy on 05/05/2022 17:54:06

having built quite a few American sourced engines my chart is the other way round but easy enough just to look at the BA colours and choose a suitable UNC or UNF number.

You may also need to look at UNEF and the Model Pipe series for some of the finer threads

Also be aware that standard UN fixings will have quite a large hex so may not fit the space available but you can get small hex from the likes of American Model Engineering, see this and the next page. When you click on the screws it shows a chart of the hex sizes

From Jason's chart, I see that 1BA is something of an "orphan" thread with no clear alternative. A nuisance because it was used extensively by Amal carburetters for their motorcycle handlebar levers and ealy carbs. Does anyone know of a closer equivalent. than the ones shown in Jason's list?

As 1BA is not commonly used for fixings being a non preferred size I did not colour match it to anything. But if you look at the numbers and just choose the nearest in the system you are using which will be M5 or #12 as Dennis says.

The #12 being closest with a 0.007" difference, M5 a little more at 0.012" smaller ( 0.3mm)

1BA is also common on gas jets. Which I would rather get 1BA taps and dies for than try and drill such tiny holes. For replacement fixings on Amal parts then you would also want to cut matching threads, or if the casting has stripped you will be wanting a bigger replacement screw anyway. These charts are more for making from scratch than restoration work.

Edited By JasonB on 06/05/2022 07:23:59

The purpose of a thread is either to provide a load to clamp components together, or a fine adjustment.

So, as close an approximation as you can get in another thread system will do the job just as well.

The easiest is M6 instead of 0BA, since then only difference is thread form.

UNF and UNF are easy equivalents for BSF and BSW.

NPT tpi usually differ by one from BSP, as well as the thread form, but are intended to perform the same function.

ANC and ANF threads should provide suitable alternatives for some of the smaller BA sizes, as would some fine pitch Metric threads.

For the latter you might have to import Taps and Dies from UK traders like Tracy Tools, or The Tap and Die Company

HTH

Howard.