Kratos Design Group M4 Receiver Extension Flat Dark Earth. Constructed of impact-extruded 7075-T6 aluminum with Type III Class 2 hard coat anodizing for an extremely hard abrasion resistant surface. Finding the perfect length of pull is easy with six adjustable stock positions. Specifications for Kratos Design Group M4 Receiver Extension: Manufacturer: Kratos Design Group Finish: Hardcoat anodize Fabric/Material: 7075-T6 Aluminum Gun Make: AR Platform Gun Model: M4 AR-15 Dimensions: 5x2x2 in Weight: 3.9 oz Package Contents: Kratos Design Group M4 Receiver Extension What firearm models does the manufacturer say Kratos Design Group M4 Receiver Extension is compatible with? The manufacturer suggests that Kratos Design Group M4 Receiver Extension is compatible with AR-15 M4Kratos Design Group RE-M4-FDE-KDG: M4 Receiver Extension Flat Dark Earth