The rear sight once graced the barrel of a Springfield musket. The long leaf has had the disc attached to it and the short leaf is present too. It could have come from an 1855, 61 or 63 and possibly some of the other Springfields too. They had a somewhat unusual dovetail at the rear and a 10-32 screw into the barrel. This one has obviously been attached with a flat head wood screw and one can only guess what they did for a dovetail.