Convert trade size knock-out holes to diameters suitable for strain relief bushings. Allow for standardization of panel design since various strain relief bushing sizes can be adapted to one panel hole size. Allow for the mounting of strain relief bushings into unusually thick panel. Adapters mount into 1/2" knock-outs (7/8" or 22,2 mm nominal diameter). Made of zinc-plated steel. For Heyco Knock-Out Seals, click here. DFARS Compliant