Measure the curve and extrapolate the diameter and it will fit whichever rifle is similar or look at the mounting screw holes. If it's flat where it meets the base it's being attached to, it's likely intended to be multi-purpose and the rail it fits on would be proprietary.
Not trying to be snide.
It could easily be an aftermarket product and made to fit several different receivers, or it could be proprietary to one type.
That's a very nicely made sight by the way. Most aren't that precise or marked that well.
From Google
Vaver Sight Co. Chicago,Illinois Dial Micrometer receiver peep sight for the Model 52 Winchester. In good functional condition. These sights were available in the 1920's and 30's