Talk:British Standard Fine

I believe that the article on British Standard Fine contains some errors in the column headers and/or the columns.

First (and of least importance), the BSC Match column contains virtually no information. Had it been headed "BSC TPI" and the tpi of the various diameters then entered, it might have been of some interest to a few people.

Second, BSF is an inch based system and all dimensions should be given in inches.

Third, the Decimal Inch column should go to 4 places. 0.19" makes a sloppy fitting hole for a 3/16" dia. screw.

Fourth, the figures are not correct for the recommended parallel jaw openings of wrenches to fit the particular bolt or nut size. It appears, after converting all of the mm back to inch, that the figures were copied out of a table giving the maximum allowable width across the flats of the hexagonal bolt head or nut in each size. However, the metric figures are mostly in error in the third decimal place (not shown) so use of the word "exact" is technically incorrect.

Fifth, the figures in the Metric column are all wrong anyway, as the minimum allowable flat-to-flat for wrenches is larger than the maximum allowable for bolt heads and nuts. My reference source quoted below does not have a table of wrench sizes for any of the Whitworth fasteners but for UNF and UNC, the minimum difference is 0.003" for 3/8" nominal diameter and 0.004" for 1/2". Probably a Whitworth table would be shifted one diameter lower as for example the head size for 1/2" BSF is the same as that for 3/8 BW (BSW).

Sixth, the column purporting to show US fractional size wrenches to safely fit BSF fasteners is mostly wrong. The sizes given will all go on but in most cases are too loose and will eventually result in damage to the bolt heads or nuts. It is too many years since I last worked on a Series Land Rover, and in any case I always maintained two or three sets of BSF/BW and BA spanners for working on them. But I think that 19/32" (used to be included in US tool sets but I never knew why) is a good tight fit on 3/8 BSF, and therefore much better than 5/8". And I think that 13/16" was a good fit for 1/2 BSF and I know that 1-1/4" fit the lug nuts perfectly. Otherwise, only the proper BSF/BW wrenches were a satisfactory fit. And the table would clearly imply otherwise.

References: Owned 6 Land Rovers since 1969 plus bought and dismantled for parts about 10 more and worked on probably 30. All but 3 were either partially or wholly BSF.

           Machinery's Handbook, 21st Edition

Robert Downs, Houston WA5CAB 76.31.44.119 (talk) 23:16, 8 February 2015 (UTC)