Browning 12511 Base System XLOCK X-Bolt 30mm Medium Black Matte Features a system that uses four screws per base replacing the traditional two-screw system. Integrated scope mounts unitize the ring and base into a single unit machined from 7000 series aluminum and eliminate alignment problems and possible loose connections between bases and rings. X-Lock bases can also use standard Browning rings. Specifications: - Tube Diameter: 30mm - Height: Medium - Finish: Matte Black