The E-Volv Battlestock cheek rest is an add-on for the standard AR-15 m4 style collapsible buttstock. The rest improves your cheek weld over the M4 stock, and also adds water-tight storage compartments. The storage compartments are designed to hold cr-123 batteries and separate them to avoid discharge and noise. The stock adaptor also features a quick-detach swivel attachment point. High strength polymer construction.