This Universal MCB Lockout has been designed to fit on almost any size of MCB, regardless of size or the position of the holes on the breaker. Simply turn off the breaker and place the lockout over the switch. Use the thumbscrew to tighten the internal grub screw onto the switch, locking the unit into place. The thumbscrew will then fold down on its integral hinge, allowing a padlock to be fitted onto the lockout preventing the thumbscrew and the unit from being removed.