Replace your factory rear sight with this large, light gathering rear ghost ring with two green, fiber optic dots for sharp contrast and quick sight acquisition in all light conditions. Ring aperture naturally centers and draws the eye to the front sight for faster target acquisition and improved accuracy. Fully adjustable for windage and elevation. Rugged, low-profile aluminum sight has an anodized finish for resistance against corrosion. Use with existing factory front sight or with Williams Fiber Optic Rifle Sight Bead. Slide mounted ghost ring fits all standard size Williams WGRS or WGOS rear sight bases. Mfg: Williams Gun Sight SPECS: Aluminum, black anodized. A 1/4" (6.4mm) high. Aperature - 5/32" (3.9mm) I.D.