ISO 866:2016规定了无保护倒角（A型）中心孔的中心钻尺寸。 它只涵盖公制尺寸，这被视为今后此类钻机的唯一建议尺寸。 根据制造商的判断，凹槽可以是直的或螺旋的。 除非另有说明，否则这些钻头将采用右手切削。 A型中心孔的推荐尺寸可通过合理使用本国际标准中列出的中心钻获得，见附录A。

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.