K21AC Marks Type Poliished Brass US3 Solid Unilock Knob / Plate Assembly Kit Thru Bolted, Replacement For Marks Mortise 21AC Ornamental Iron Gate Door Lock, Typically used on mortise locks. Each spring loaded spindle is 9/32" square. Set is thru bolted and includes screws for both 1-3/8" and 1-3/4" doors. Replaces Marks USA #21AC Mortise Lock Knobs. Knob and Plate are pre-assembled. Packed one pair per box.