Hawks Tech Tactical Hunting Holographic 1 x 40mm Airsoft Red Green Dot Sight Scope 11 & 20mm Rail Mount Objective Diameter: 36 mm, Tube Diameter: 40mm 5 Level Brightness Control Compatible for 11mm & 20mm Weaver Rail Powered by volt lithium battery (CR2032) Length: 96mm Material: High Grade Aluminum Alloy