A knockout punch is an electrician's favorite tool when he needs to make a hole in an electrical box or panel. A knockout punch set gives you the choice of many different sized knockouts to make different sized holes. Some sets have a hydraulic pump to make punching the holes very easy, while others, like the set shown, have a large bolt head that you must use a wrench or socket to turn in order to make the punch do its work.
Knockout punches come in two parts: a cutter and the cutter guide. Knockouts like this one are called slug busters because the cutting tool actually cuts the metal hole in half. The cuter is used to cut through heavy sheet metal, stainless steel, plastic, and fiberglass. Although hole saws will also cut a hole, the knockout punch makes a nicer and neater installation hole.
To use a knockout punch, you must first drill a hole, using with a ½” hole saw to allow the knockout punch bolt to be inserted. Then simply slide the punch guide over the bolt and stick the bolt through the hole. Now screw on the cutter blade until snug. Using a wrench or socket, turn the bolt head clockwise to draw the cutter through the metal you are trying to punch through. Once the hole is punched, unscrew the cutter and remove the cut pieces.