I need some help identifying this Lyman receiver sight, it's mounted on a Winchester Model 52 from the early 1950s. No model number that I can find and an internet search has not provided anything.
Looks to be a definite Lyman Peep Sight. The ones on similar small caliber Winchesters are usually the Lyman Model 90MJT but a lot of years have gone by. Call Lyman and tell them which gun and serial number you have and they will probably give you the Model # for the one you have or its replacement. I have a Winchester Model 1894 and they were even able to provide me with replacement parts for repairing a sight from the 1950s.
Here is a link to the new style Lyman Model 90 sight.