I have the Beeman (made by Williams) aperture on my Beeman R7. And some blue Lock tite is highly advised. I also replaced the front sight with one that allows interchangeable inserts and find I like the fine post best.
It just clamps onto the dove tail grooves on the receiver of the R7. Its hard to get it as far to the rear as I would like but it works pretty well.
The Beeman model is just more sleek and tidy than the one Williams sells directly. I have a Williams one on a CZ .22 lr Scout youth rifle. Had to cut away the stock to make that one fit and still needed to replace the front sight with a higher blade. On the aperture base I replaced the allen head screws with long heavy slotted head screws so I could cinch it down more easily - the allen heads were so small it was too easy to round out the socket without getting the base tight enough.
And I have Williams peeps on a Marlin 39A .22 and my Win mod 94 30-30.
Hmm I see Straight Shooters has raised the price on the Beeman aperture:
Beeman Adjustable Sport Aperture Sight.
Includes finger adjustment knobs
Take a huge step up by clamping on one of these small but elegant aperture sights. The right side of the mounting dovetail can be fitted exactly by simply tightening hidden precision lock screws onto the male receiver grooves of most adult air rifles. These units allow the sight to be switched from gun to gun (even different makes), and can be attached to guns which have receiver grooves that are not open to the rear, such as the Webley Hawk or Vulcan air rifles. Securing screws bear against this sights clamping jaw, not against the gun. Positive click micrometer adjustments can be locked securely. The target knobs on the deluxe version are a welcome addition for shooters who prefer the convenience of readily turned knobs. Built of rust proof alloy with a tensile strength of over 85,000 lbs., it is compact and weighs only 1-1/2 oz. Special anodized deep blue-black finish is extremely durable. No machining required - just slip onto receiver grooves and tighten the allen screws with the wrench provided.
Instantly fits air rifles with built-in scope grooves. (FWB, Beeman, HW, Hy-Score, Fl Game, old and new Webley, Winchester, RWS, Geco, Sharp, Marksman, BSA, BSF, etc.)
Catalog No. 5823
See:
http://www.straightshooters.com/beeman/bapadspt.htmlyou might try D&R Sports - a Gray Beard advertiser - they may be able to get the same sight and maybe for a better price.
Or try the Beeman site:
http://www.beeman.com/apertures.htm