protect an electrical box and maintain fire-resistance ratings of wall assemblies, when the horizontal separation between metallic boxes on opposite sides of the wall is less than 24" (610 mm).
Tested in boxes up to 4-1/2 in. x 14 in. x 2-1/2 in., Suitable for steel and plastic face plates., Easily pre-installs before shipping to the jobsite., Eliminates the need for putty.