Have the security of knowing you always have a spare 20-round mag. Includes A2 Stock Mounting HardwareUS Tactical Systems Back-up Twenty With A2 Installation Hardware Have the security of knowing you always have a spare 20-round mag as back-up just in case other ammo sources are not available. The BACK-UP TWENTY™ buttstock adds minimal bulk to the overall weapon, yet the extra magazine may be the difference between life and death. Constructed of durable Dupont® Zytel®, the stock retains the spare magazine using the same latching mechanism as the regular M16A2. The magazine is securely stored in a dust-free environment until the trap door is deliberately opened and the magazine release button is pushed.This stock replaces the standard M16A2 or AR-15 buttstock and maintains the weapons existing handling characteristics. Includes a standard size sling loop. Includes Back-up Twenty A2 Installation Hardware Installs on any AR-15 or M16 lower receiver to accept the A2 style Back-Up 20 Stock. This kit includes everything needed to get your Back-Up 20 installed in minutes. Includes Buffer, Buffer Tube, Spring, Stock Extension Cap, and hardware. This kit is a standard size, so it will work on other AR-15 and M16 A2 stock installations as well. Save money by purchasing together! 20 Extra Rounds Durable Dupont Zytel Push Button Design Mounts On M16A1 or AR-15