A concave knob with a "pineapple" in the center. Knob design patent #D17,339 and escutcheon-plate #D17,338, May 10, 1887 by George S. Barkentin, assigned to P & F Corbin. Entry knob has a diameter 2 1/2 inches, interior knob 2 1/4 inch. Both knob and plate shown in 1895 Corbin catalog page 621 Click on each photo below to view additional images and information