BTF
07-14-2009, 10:31 AM
The following blurb can be found here:
http://www.hot.net.au/~kht/
British spanners are complicated in their markings. Early Whitworth nuts and bolts were larger than British Standard nuts [ BSF-BSCY] for example, a 5/16 Whitworth nut was the same size as a 3/8 British Standard nut. This meant that early spanners were marked one size too big for modern nuts, later they were marked in both Whitworth and British Standard i.e. 5/16
Whitworth 3/8 British Standard.
Later on, Whitworth was changed to B.S.W. [British Standard Whitworth] and the nut size was the same as BSF for the same diameter bolt. and the spanner carried one marking either BSW or BS. Make sure you are buying the right size spanner for the head size.
American spanners are much simpler, early spanners were marked with diameter, followed by SAE i.e. 3/8 SAE. Later spanners are simply marked AF, which means across flats. A 7/16 AF spanner fits a nut which is 7/16 across the flats of the hex head. A 7/16 AF fits a 1/4" inch bolt, 1/2"AF fits a 5/16 bolt and so on.
http://www.hot.net.au/~kht/
British spanners are complicated in their markings. Early Whitworth nuts and bolts were larger than British Standard nuts [ BSF-BSCY] for example, a 5/16 Whitworth nut was the same size as a 3/8 British Standard nut. This meant that early spanners were marked one size too big for modern nuts, later they were marked in both Whitworth and British Standard i.e. 5/16
Whitworth 3/8 British Standard.
Later on, Whitworth was changed to B.S.W. [British Standard Whitworth] and the nut size was the same as BSF for the same diameter bolt. and the spanner carried one marking either BSW or BS. Make sure you are buying the right size spanner for the head size.
American spanners are much simpler, early spanners were marked with diameter, followed by SAE i.e. 3/8 SAE. Later spanners are simply marked AF, which means across flats. A 7/16 AF spanner fits a nut which is 7/16 across the flats of the hex head. A 7/16 AF fits a 1/4" inch bolt, 1/2"AF fits a 5/16 bolt and so on.