Heat Fab Essentials 8" Insul-Plug - Premium Insulated Electrical Plug for Home & Industrial Use - Perfect for HVAC, Appliances, and Power Tools

The Insul-Plug blocks old, unused thimble holes in masonry chimneys. It provides a thermal break from combustibles and prevents downdrafts from entering the room. The Insul-Plug is constructed of a ceramic based fireproof insulating material. The black outside plate covers up to a 10" diameter hole. Simply insert it in the old thimble opening and tighten the expansion screw on the face of the Insul-Plug. The sides expand and create a tight fit inside the thimble opening. It can be removed by reversing the process. Features: Type: Insul-Plug. Specifications: Overall Dimensions: 8" (W). Adjustable: 7 3/4" to 8 1/8".