Z-M Weapons AR-15 Accu-Wedge can help make any Ar-15 more accurate and consistent. This wedge fits between the upper and lower to make them both solid and more accurate. The wedge specifically goes in the rear of the lower, behind the push pin. The best part about this addition to your weapon is that it doesn't require any modifications. Made of a long wearing rubber, this wedge will last the lifetime of your weapon.