The FAB Defense GLR-16 Buttstock for your AR15/M16 provides you with enhanced versatility with it's stock extension and optional adjustable Cheek Rest. FeaturesNon-Slip Unique Traction Design Rubber Butt Pad, Allows Fast and Stable Shoulder PositioningThree Integrated Slots for Sling Attachment, One in the Front and Two at the RearSealed Storage Compartment for Two CR123 or AA Batteries with a Rubber Fixation that Eliminates Rattling NoiseIntegrated Ambidextrous Quick Detach Swivel Rear Sling ConnectorsEnhanced Non Slip Quality for Steady Positioning with Body ArmorMaintains Contour & Size of Original DesignUnique Patented "Anti-Rattle" Mechanism allows fit on Both Tubes; MIL-SPEC and Commercial AftermarketAdjustable Cheek Rest Allows Optimal Comfort and Accuracy