The revolutionary patented 'GL-Shock' absorbing Buttstock contains a recoil-reducing mechanism with a built in premium silicon chrome alloy spring creating a State-of-the-Art stock for your M4/M16. - Advantages: - Unique Patented �Anti-Rattle� Mechanism - Sleek New Design with No Protruding PartsWill Not Get Caught on Gear and Webbing - Unique New Slick and Quick Operated Inversed Positioning Lever - Integral Ribbed Rubber Butt Pad with a Non Slip Design - Integrated Quick Detach �QD� Sling Swivel Connectors on Both Sides - Watertight Battery Storage for Two CR123A 3V Lithium Batteries / AA 1.5v - Fits Perfectly on Both Tubes - MIL-SPEC and Commercial Aftermarket! - Made from Mill-Spec Reinforced Composite Polymer - With an Adjustable Cheek Rest.