02-09-2020, 06:14 PM
Howard, here is a chart that gives diameters of most of the available BA sizes. I suppose it is possible that Smiths may have cut their own threads, but I doubt they would have done that. Sizes of BA go up(down) to the smallest at 25BA, which I'm not sure my old eyes could even see.
Erich in Seattle
https://maccmodels.co.uk/ba-size-chart/
Erich in Seattle
https://maccmodels.co.uk/ba-size-chart/