Thistle Door Knocker. The thistle is one of the better known symbols of Scotland. The door knocker swivels on a Celtic design base and the striker plate also is cast with a Celtic design. Measures 5 1/2″ X 5 1/2″. Two holes are required for installation. Capped mounting studs are also included. Solid Brass. 2 screws approx. 3/8 inch in diameter and 2 5/8 inches long and can be cut to fit.