Magpul

-Mounts on mil-spec sized carbine receiver extension tube (not included) from manufacturers such as Colt, Armalite, S&W, LMT, & others (please see the note below)-Two water-resistant battery storage tubes located on the left & right sides of the stock -Each tube will store up to two (2) CR123A lithium or AA batteries -Tubes are accessible from the rear in any stock position via a hand-removable rubber plug-Supplemental friction lock minimizes accuracy robbing wobble*-Premium chrome-silicon lock spring provides positive locking & long service life-Sloping cheek weld provides a wide contact surface for user comfort-Shielded release latch prevents snagging & accidental operation-Replaceable 0.30" Rubber Butt-Pad offers an anti-slip surface& increases impact protection-Compatible with Magpul ASAP®,ASAP® QD, & other receiver-mount sling attachments-Sling Mounts -Rear -Reversible Type 1 Sling Mount fits up to 1.5" push-button QD swivels (swivel not included) -Rear/Bottom - 1.25" sling loopsNote: There are two basic sizes of M4 Carbine receiver extensions (buffer tubes): mil-spec & commercial-spec. If you have a commercial-spec extension on your rifle, make sure to order #MAG471* Friction lock performance may vary depending on the host receiver extension's dimensional tolerances.** Specifications based on standard-length (flat-back) M4 Carbine receiver extension & may vary depending on tube manufacturer.