Similar to the Lancaster sideplates with a pointed tail, this sideplate is typical of those by Herman Rupp and other makers of the Allentown-Bethlehem region.
For L&R Dickert or Siler's large lock. Easily shortened to fit popular smaller locks. Cut sheet brass, made in the U.S.A.. Overall length 4-11/16", height 1-1/16", thickness 0.080".