What is a Knockout?

A knockout is a general term used to reference any pre-scored removable section that is intended to be cutout during installation. Most frequently, the term will be applied to electrical wiring harnesses and cutouts. When the manufacturer designs a wiring harness, they tend to try to make them as versatile as possible since the intention is that it can be used in a wide variety of projects. To accomplish this, the casing will have several cutouts that have been scored into the sides of the wiring box. These are typically standard sizes that will match up with other pieces like conduits or flex hose. The advantage is that there are several different options to choose from at the time of installation.

When purchasing one of these wiring harnesses with multiple knockouts in it, one will have the option of only removing the pieces that need to be removed to accommodate a particular project. For example, the wiring box may have a circle scored into all four sides, but if only two wires need to be brought into the box then only two of the four knockouts would be pushed out. Knockouts make it easier on the installer because the options are all there so only a few seconds are needed to make a hole precisely the right size instead of having to take the time to cut it out.