a spanner (wrench) marked <i>7/16BSF</i> is the same size as one marked <i>3/8W</i>. In both cases the spanner jaw width of 0.710&#160;in, the width across the hexagon flat, is the same. However, in World War II the size of the Whitworth hexagon was reduced to the same size as the equivalent BSF hexagon purely to save metal during the war, and they never went back to the old sizes afterwards. Thus it is today uncommon to encounter a Whitworth hexagon which takes the nominally correct spanner. Spanners in th