目前关于切制螺纹前孔径的标准,大多沿用苏联书籍(如机械加工手册,工艺师手册等)推荐的数值。该标准按材料性质同一规格的钻孔直径不同(个别相同),这是由于不同材料塑性不同之故。区分为两种是为了要使切制螺纹后的孔径达到预定的要求,然其差升甚微(0.1～0.2)。例如:M12切制螺 At present, most of the standards for cutting the pre-thread aperture are based on the values ​​recommended by Soviet books (such as machining manuals, craftsmen’s manuals, etc.). This standard by the nature of the material of the same specifications of the drilling diameter is different (the same as the individual), which is due to different plastic material so different. Divided into two is to make the thread after cutting thread to meet the predetermined requirements, however, the difference between the rise of small (0.1 ~ 0.2). For example: M12 cut screw