To BA, or not to BA

[houstonceng]

One advantage of BA and Whitworth form threads, over Metric and SAE, is that the smaller included angle of the thread makes for stronger fixings in cast iron and soft materials like aluminium.

[Roger]

Nov 2, 2015 21:32:16 GMT houstonceng said:

One advantage of BA and Whitworth form threads, over Metric and SAE, is that the smaller included angle of the thread makes for stronger fixings in cast iron and soft materials like aluminium.

I'm not sure that's true. If you look at the BA sizes and pitches, they are very similar to Metric coarse threads. The big advantage of Metric is that you don't have many different standards that do pretty much the same thing. My Metric collection of Taps and Dies covers the same range of sizes, but I've got about three times as many items in my Imperial drawer to achieve exactly the same thing.

[houstonceng]

A 47.5 or 55 degree included angle will always give a deeper thread than a 60 degree angle for the same TPI. That's why a lot of cars had Whitworth threads in the cast iron exhaust manifold with, in some cases, a metric thread on the other end of the studs.

[abby]

Quite correct Andy, the chosen angle was not accidental but developed after much experimentation.