Stuart Threads

Hi Steve,

I have done a number of Stuart Turner restorations and have noticed that some of the older engines I have worked on use BSW as opposed to BA threads.
Would  you know approximately when Stuart Turner went completely over to BA?
Excellent website by the way it has been a great help to me!

Kindest regards


Hi there Shaun, 
A very interesting question with a possibly more interesting answer.
First thing, about BA threads.


BA (British Association) screw threads are named after the British Association for Advancement of Science and were put together in 1884 and standardised and published in 1903. Screws were described as 2BA, 4BA, 6BA and 8BA; the bigger numbers denote smaller screws.

This gives us a starting date of
1884 so ST could have started with BA threads as his first advert in Model Engineer is 1901. 

The problem is this, when you have a workshop you fill it with tools like taps and dies. These tools are semi disposable as they tend to break. When a new system is released you have to decide when to upgrade at a cost. If plans move to the new system you can convert them and continue with old system, (o have a couple of sets of plans where every dimension has been replaced and this can cause figment problems) but it becomes a chore. You can upgrade as breakages occur spreading the cost or you can splurge the cash. 
This situation occurs both for the designer and the machinist. So even if plans are in BA a machinist may still use BSW. So the machinist could build an engine in any year he decides to keep using BSW.
As far as ST goes where could we look to find out when.
The best place would be drawings but getting hold of old drawings is very unlikely, even Stuart do not have plans for all their engines, including some surprisingly late ones.
The next best place is catalogues both for mentions in descriptions and selling them in the back.

The earliest catalog I have access to is 1906 and it sell BSW taps and dies.

1926 catalogue sells BSW, brass gas, iron gas & Model Engineer taps and dies. Special taps are mentioned , made in house, short thread section but stronger. BA threads included. Bolts sold are all BSW but brass screws are available in BA. 
This seems to me that ST is still committed to BSW for construction but accepting the spread of BA.

1933 catalogue full set of BSW bolts, nuts, studs. Full set of BA bolts, nuts, studs. No mention of BA taps and dies even in the special taps section. 
It seems that ST now accepts the useage of BA fittings but still is using BSW for construction.

1957 catalogue BA nuts, bolts, studs. Taps and dies BSW, brass gas, Model Engineer, BA.
Seems that now ST has transitioned to BA threads. The listing order of taps and dies with BSW listed first is almost certainly because the table, set out as a comparison, most sizes available in BSW less so in the other formats.

So sometime between 1933 and 1957 is as close as I can get to tying down the changeover date. Someone with access to other catalogues would have to do a bit more research. Certainly I have ST models from around the 1940’s that still use BSW. 

I am thinking of adding a questions and answers page so I can where these ideas, keep an open as I will add in a request for more info from the readers.



Hi Steve,

Many thanks for the detailed analysis, very interesting indeed.
Do you know I asked the same question to Stuart Turner and they are surprisingly clueless.
The answer I got back was they think early engines built with BSW are all pre-WW1, but not sure!
I would have said pre-WW2 as you have pretty much concluded.
I have an early 10V with standard & rod and an early 10H, both started manufacture in 1924 and both BSW.
Anyway please keep up the good work, I find it extremely interesting and also keep safe.

Kindest regards