I've used William receiver sights since the early sixties and have them mounted on several of my rifles today. Though most of them are the "FoolProof" variant (having micrometer adjustments, coupled with set -screws), it might be useful for some to know that the "5D" model (a moniker reflecting the original price of five bucks) is essentially the same sight as its considerably higher priced cousin (the FoolProof), sans micrometer adjustments. If plan on sighting-in and not changing the setting often, if at all (like many, if not most of us do with our hunting rifles), the 5D is all you'll ever need.