Drilling is important, to draw a line as well as tags, so-called eyes, in particular the four corners are mutually perpendicular axes, such as eye playing Askew, it is not straight splint.

• 打目是轻给的一环，给画线息好标志，目给打侧，出格是四个角都给彼此笔直，如目打歪了，夹板不即不拆不侧。