Riser is attached to the top rail and raises rail segment 1 above the rail. Compatible with standard 20mm Weaver / Picatinny 1913 accessories. External part is simply bolted on with a hex screw. Made with black anodized aircraft aluminum material for durability. Dimensions are measured out to 1.60 in length and 1.25 by height. In the Box Riser Mount Specifications: California Proposition 65 Warning: Cancer and Reproductive Harm - www.P65Warnings.ca.gov