The dovetail block is used to mount the William Malcolm short and long scopes. It fits into the existing dovetail on your rifle.
You may need a different sized dovetail block for your rifle if you are using any of the following mounts:
Henry Golden Boy .22 Mount (HGB22MT)
Winchester 73-76 Mount (W7376MT)
Winchester 1885 Mount (W1885MT)
Winchester 92/94 Side Mount (W9294MT)
Sharps Side Mount (SHSMT)
Round Barrel Offset Mount (RBOSMT)
There are 3 sizes of dovetail blocks available - 3/8" (DB0375), 1/2" (DB0500), and 5/8" (DB0625).