255mm diameter with fixing and sensory holes. This escape provides very rapid clearing. It requires pinning into a 50mm deep chamber board. This is simply 4 laths of timber 50mm wide tacked to a sheet of 6mm plywood. Cut a 75mm diamteter hole central in the board and put the escape inside the chamber with the central void of the escape over the hole cut in the plywood. To use simply place the board, escape side down, under the super to be cleared.