ISO 237:1975

Rotating tools with parallel shanks — Diameters of shanks and sizes of driving squares

Applies to reamers, screwing taps, etc. It comprise two series of dimensions. The complete range of diameters is divided into a certain number of diameter steps. In the metric tables, the values of the across flats of the squares and the preferred diameters are scaled in accordance with the R20 series of preferred numbers. In the inch tables, these values are exact conversions of the corresponding metric values.