(1) Non-circular projection views often adopt full section or half section, and draw a thin dotted circle and a symmetrical center line at the position where the worm line is engaged to mark the relevant dimensions and center distance. (2) In the view projected as a circle, only the largest top circle and graduation circle are drawn, and the throat circle and tooth root circle are omitted. The projected circular view can also be replaced by a partial view showing the keyway shaft hole.