Compact, Low Profile, Lightweight, Strong, Rustproof, Positive Windage and Elevation Locks. In most cases these sights utilize dovetail or existing screws on top of the receiver for installation. They are made from an aluminum alloy that is stronger than many steels. Light, rustproof. Williams quality throughout. NOTICE: ALL WGRS RECEIVER SIGHTS ARE FURNISHED WITH THE STANDARD R-3/8 X .093 LONG SHANK APERTURE. ALL OTHER SIZES OF REGULAR AND TWILIGHT LONG SHANK APERTURES ARE AVAILABLE AS ACCESSORY ITEMS.