A knockout refers to a pre-scored section that is meant to be removed during installation. This term is commonly used in reference to electrical wiring harnesses and cutouts. Wiring harness manufacturers strive to create versatile products that can be used in various projects, which is achieved by incorporating several scored cutouts on the casing of the wiring box. These cutouts are usually standard sizes that match other components such as conduits or flex hoses, providing installers with multiple options to choose from during the installation process.

When purchasing a wiring harness with multiple knockouts, installers have the flexibility to remove only the required pieces to accommodate a specific project. For instance, a wiring box with a circular knockout on all four sides may only require two knockouts to be pushed out to bring in two wires. Knockouts make installation easier and quicker as installers do not have to spend time cutting holes to the correct size; the options are already available to them.