Trinity Door Knocker. The Trinity Knot is as impressive to look at as it is functional. The door knocker swivels on a Celtic design base and the striker plate also is cast with a Celtic design. Measures 6″ X 6″. Two holes are required for installation. Capped mounting studs are also included. Mounting Hole Spacing = 5″ on Vertical. Solid Brass. 2 screws approx. 3/8 inch in diameter and 2 5/8 inches long and can be cut to fit.