British Standard Whitworth
（重定向自Whitworth thread）
![Whitworth thread form](/Images/godic/202502/21/Whitworth0723.jpg")
![Two spanners, both nominal size, 5/8 in, with a diagram superimposed to show the logic that allows them both to be nominal size 5/8 in when their actual sizes are clearly different (across-flats distance vs screw diameter). The across-flats definition is the common standard today, and has been for many decades. The larger spanner in this photo is from the 1920s or earlier. Its face was polished to allow the size stamp to show well in the photograph. This example is American, but it illustrates the way that spanners for Whitworth fasteners were typically labelled.](/Images/godic/202502/21/5-8_vs_5-8_0030723.jpg")
British Standard Whitworth (BSW) is one of a number of imperial-unit-based screw thread standards which use the same hexagonal bolt head and nut sizes, the others being British Standard Fine thread (BSF) and British Standard Cycle. These three are collectively called Whitworth threads.