The UTG Model 4 is a complete A2 rifle-length fixed stock assembly for the AR-15 - everything you need to convert a lower receiver to a full-length M16A2-style buttstock in one kit. Whether you are building a featureless configuration for a restricted state, running an A2 clone, or you just prefer the solid feel of a rifle-length stock over a collapsible carbine, this kit ships ready to install straight onto the receiver. Specs and features: Complete A2 rifle-length stock assembly for AR-15 Includes 4.8 oz rifle-length buffer, action spring, receiver extension, buttstock, stock spacer, butt plate, and stock screw Fixed, non-collapsing - legal in featureless AR-15 configurations Storage compartment in the buttstock for a cleaning kit or small AR-15 parts Black finish, drop-in fit on any standard AR-15 lower receiver Compatibility: fits standard AR-15 lower receivers with the A2-style buttstock takedown detent hole (all mil-spec lowers). Because this is a rifle-length assembly (not carbine), it uses the longer A2 receiver extension included in the kit - do not mix with a carbine buffer or spring. Firearm configuration laws vary by state; verify local regulations before building.