The user shall cause every grinding wheel of a power-driven grinding machine to be mounted concentrically on the spindle by means of robust metal flanges with annular peripheral bearing surfaces of adequate breadth, which shall bear upon the wheel, and a layer of suitable compressible material to be fitted between the flanges and the wheel: provided that grinding wheels for specialized application that cannot be fixed by flanges shall be so secured that displacement or rupture of the wheel in motion is eliminated as far as possible.