Lehman Archer and B.A. Taps:
I enjoyed the article, particularly as it is based on original materal.
The quotation from the LA catalogue gives the BA thread angle as 47 degrees; I had always understood it to be 47.5 and wonder whether this is a typo or, perhaps, there was a further change to the specification.
BA threads have metric pitches and it is interesting to see that the catalogue also gives a TPI equivalent. On the accuracy point, I would have thought that introducing a 127T gear would have allowed theoretical perfection. Is the "correct to within 1/53,300th" a reflection of the then state of the relationship between inch measure and metric? I believe it is only relatively recently that the 1" = 25.4mm equivalence was settled.