It's cleary a small frame sight with its vertical serrations on the back.

There are three I & J frame post war micro click rear sight sizes (over-all length):

1. The 1953 New I frame =2.390-95” long; this one has the front mounting hole 1/16” further back.

2. The Mod 34-1 '60s and '70s J frame = 2.530-35” long; 22/32 M 34-1 and Mod 36 target.

3. And the most current J frame = 2.718” long;my M 60-4 (1990), my M 36-6 (1986) and 22/32 M 34-2 (1980) and the M 63.

__________________
Jim
S&WCA #819