Brian Albinson contributed: >In 1884 the British Association for the Advancement of Science adopted a >thread form and series, primarily for use in precision equipment. It was >inspired by one used in the Swiss watch and clock industry, and was >formerly sometimes called the Swiss Small Screw Thread System; but is >now just referred to as the BA series. Like the Whitworth thread, it has >a rounded root and crest, but the included angle is 47.5 and the radius >is 0.1818Ö times the pitch.
My version of events is that the BA system of screw threads was proposed in 1884 but not actually adopted until 1903 so this may make a difference to your dating John. Tony Moss. -
