The Magpul STR (Storage/Type Restricted) Carbine Stock Mil-Spec is a drop-in replacement buttstock for AR15/M4 carbines using Mil-Spec sized receiver extension tubes. A storage-capable version of the CTR , the STR has improved cheek weld and two water resistant battery tubes on a compact, reinforced polymer A-frame design. A shielded operation lever and supplemental friction locking system prevent accidental operation and minimize excessive stock movement for enhanced weapon stability and accuracy.* The STR incorporates two integral sling loops, a reversible push-button QD sling mount, and a replaceable 0.30" thick rubber butt-pad which provides positive shoulder purchase to prevent slippage even with body armor or modular gear. Product Specifications Platform: AR10, AR15, M4, M16, M110, SR25 Compatibility: Mil-Spec sized carbine receiver extension tube (not included) from manufacturers such as Colt, Armalite, S&W, LMT, and others LOP, M4 Collapsed: ~10.9 in. LOP, M4 Extended: ~14.2 in. LOP Adjustment Range: 3.3 in. Length, max: 7.3 in. Weight: 12.3 oz. Weight, w/ receiver extension: 16.3 oz. Width, max: 2.6 in.