Re: Gnomons and screws

[Brian Albinson]

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 47.5ƒ and the radius 
is 0.1818Ö times the pitch.

Brian Albinson


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