Parallel and taper keys and keyways for shafts of 6 mm to 500 mm diameter. For square and rectangular parallel keys three classes of fit, 'free', 'normal' and 'close', are foreseen.
BS 4235-1:1972 history
0000 BS 4235-1:1972(1999)
1972BS 4235-1:1972 Specification for metric keys and keyways - Parallel and taper keys