Precision construction and finish: Built from aircraftgrade aluminum alloy with a black hard coat anodize finish for durability and long service life. 11 mm to 21 mm rail conversion: Converts an 11 mm dovetail to a 21 mm Picatinny rail. Base length is 2.94 inches, and the Picatinny rail extends 3.94 inches to provide extra space for flexible optics placement. Mount base compatibility: Designed to fit 11 mm dovetail mounts. Includes a converter adapter from 3/8 inch to 7/8 inch. Lowprofile 0.59 inch riser height keeps the optic close to the bore line. rail features: surface features a 9slot Weaverstyle rail. The is a 21 mm Picatinny rail suitable for mounting Picatinny or Weaver standard scopes, red dot sights, or other accessories. Practical use scenarios: 1) Upgrade a rifle or other equipment with an 11 mm dovetail mount by adding a 21 mm Picatinny rail to support a red dot or compact scope, allowing flexible eye relief and improved aiming capability. 2) Attach ancillary optics or devices such as laser sights, lights, or other accessories on the 21 mm Picatinny rail for enhanced versatility in lowlight or tactical environments. 3) Use the 9slot Weaverstyle rail to mount additional accessories or backup sights, while maintaining a lowprofile base and compatible 11 mm dovetail foundation for quick accessory swaps.