A KO, knockout, is a pre-scored round section in the wall of a box, panel or enclosure sized for a conduit trade size, often made as concentric rings so one opening can grow from 1/2 to 3/4 or 1 inch. It is started with a screwdriver and twisted off with pliers. Unused open knockouts must be closed with KO seals, and where no knockout sits in the right place, a knockout punch makes one.
Use the top KOs on that can and leave the back ones for the low-voltage guys.
Popping the wrong ring of a concentric KO leaves a hole too big for the fitting; the fix is a reducing washer, and inspectors notice.
Also heard as
- knockout
- KO hole
Related terms
Slug
Metal disc knocked or punched out of a box or panel, which ends up underfoot and in the bottom of every panel.
Knockout punch
Punch and die set that shears clean round holes in boxes and panels for conduit fittings.
Four-square box
Square steel box, 4 inches on a side, that takes a mud ring or cover and serves as the workhorse junction and device box.