1.Used as the clearance holes for K.O. retainer/coupling.
2.the location and size of knockout holes for Inch Mold:
3.the location and size of knockout holes for Metric Mold:
4.The screw for K.O. retainer(1/2-13UNC or 5/8-11UNC.) should be machinined per the following diagram unless otherwise specified for Inch mold:
5.The screw for K.O. retainer(M16) should be machinined per the following diagram unless otherwise specified for Metric mold:
6.The mistakes that the beginners often makes was shown below: