Defender Security U 9517 Lock Back Plate, 3-1/2-Inch, Chrome Plated, 2-Pack Nickel plated steel construction Used with 2-1/8in. bore lock sets Covers marred doors Allows conversion of 2-3/8in. to 2-3/4in. backset Also can convert 2-3/4in. to 2-3/8in