Marble's barrel-mounted #30 Universal rear sight incorporates a sloping uni-base with interchangeable peep, semi-buckhorn or fiber optic sight blades (sold separately) available. The sight is precision adjustable for both windage and elevation, with highly visible graduation lines and tension locking screws. Elevation adjustment has also been improved with a new, push-button system that allows for quick changes in the field without tools. Sights are available that mount to round or octagon barrel profiles. All parts are CNC machined for strength and precision. Fiber optics are UV-protected for long life. Sights offer .490" to .675" height adjustment and 1/2" to 1" hole spacing.