Magpul ACS® Carbine Stock – Mil-Spec ,have a battery storage tubes on each side which is water-resistance , hols up to 3 CR123A or AA. also include an extra storage compartment at the end of the stock ,reversible QD cup ,footman loop ,ambidextrous release latch ,Anti-slip rubber butt-pad ,this rifle stock is in like new condition ,and is for a mil-spec carabiner extension tube.