孔的直径与深度之比称为长径比，长径比大于60的孔称细长孔，有细长孔的零件一般分为两种：回转体零件和非回转体零件。前者的孔可在深扎设备及车床上进行加工，后者只能在钻床与镗床上加工。对于小直径的细长孔只能用接杆钻进行加工，常用的接杆麻花钻是铜焊结构，由于麻花钻 The ratio of the diameter to the depth of the hole is called the aspect ratio, and the hole with the aspect ratio greater than 60 is called the elongated hole. The parts with the elongated hole are generally divided into two types: the rotary body part and the non-rotary body part. The former hole can be drilled in deep-hole equipment and lathes, the latter only in the drilling and boring machine processing. For the small diameter of the elongated hole can only be used to drill rod, the commonly used rod twist drill is brazed structure, the twist drill