This International Standard specifies the dimensions of centre drills for centre holes with radius form — Type R. It covers only metric dimensions, regarded as the only recommended dimensions in the future for this type of drill. The flutes may be straight or spiral at the option of the manufacturer. Unless otherwise stated these drills will be right-hand cutting. This International Standard includes an Annex giving the recommended dimensions for the centre holes. Type R, which can be obtained by a rational use of the centre drills listed in this International Standard.