ISO 866:2016 specifies the dimensions of centre drills for centre holes without protecting chamfers (Type A). It covers only metric dimensions, which are regarded as the only recommended dimensions in the future for this type of drill. The flutes may be straight or spiral, depending on the manufacturer's discretion. Unless otherwise indicated, these drills will be right-hand cutting. Recommended dimensions for Type A centre holes, which can be obtained by a rational use of the centre drills listed in this International Standard, are given in Annex A.