Internal micrometer adjustments lock positively to prevent accidental movement of sight setting. No obstructions to impair and blot out shooter's field of vision. Weighs only 1A 1/2 oz. Standard hole spacing to fit rifles factory drilled and tapped for receiver sight. Mfg: Williams Gun Sight SPECS: FP-GR-TK: 25/32" (5.5cm) wide. 15/8" body. Blued steel "Target Knobs" adjust windage and elevation. Blued steel aperture. .093" (2.4mm) opening.