Sigma Engineered Solutions 0.5-in Plastic Electrical Box Knockout Plug in the Electrical Box Knockout Plugs department at Lowes.com
TayMac 0.5-in and 0.75-in Gray Metal Electrical Box Knockout Plug in the Electrical Box Knockout Plugs department at Lowes.com
Appleton K0100 Knockout Plug | Standard Electric Supply Co.
Halex 3/4 in. Knock-Out Seals (4-Pack) 26072 - The Home Depot
Halex 3/4 In. 3-Piece Knockout Seal (4-Pack) - Kellogg Supply
Halex 3/4 in. Knock-Out Seals (4-Pack) 26072 - The Home Depot
Amazon.com: (10 Pack) 1-1/4" ID Hole Knockout Locking Plugs for Panels - Nylon Plastic 1.25 Inch ID Round 1-3/8" Head Diameter - for Panel Thickness .016" - .125" | Body n Sheet