GB/T 20330-2006 in English

《GB/T 20330-2006攻丝前钻孔用麻花钻直径》由TC91（全国刀具标准化技术委员会）归口，主管部门为中国机械工业联合会。
本标准规定了用于正常旋合长度的丝锥攻丝前钻孔用麻花钻的直径。 本标准适用于攻丝前钻孔用麻花钻。

Scope

This standard specifies the diameter of twist drills for drilling holes before tapping for taps of normal screw-in length. The diameter of the twist drill is approximately equal to the nominal diameter (major diameter) of the thread minus the pitch. The listed drill sizes are applicable to the following threads: ——Common thread (coarse and fine thread series) of GB/T 193-2003: Table 1 and Table 2; ——Inch thread of ISO 263-1973 (UNC and UNF) ; Table 3 and Table 4; - GB/T 7306.1-2000 and GB/T 7307-2001 pipe thread: Table 5 and Table 6.