Collapsible M4/M16/AR15 Buttstock fits Mil-Spec M4 Buffer Tube (available separately). This five position telescoping stock has two storage compartments with O-ring sealed screw in caps. The storage compartments are water tight and will hold two AA or three 123 Lithium batteries in each side. The stock has a nonslip hard rubber butt plate and three places to attach a sling These stocks have a life time warranty and are built tough enough so you never have to use it (the warranty, that is).