This Aero Precision Barrel Shim Kit for the AR-15 is designed to work with the AR-15 BAR barrel nut. It will not work with .308 Win and 6.5 Creedmoor barrels or barrel nuts. Includes 8 shims 0.001" in thickness. Note: This product is already included with the Aero Precision AR-15 BAR Barrel Nut. It is not necessary to be purchased separately. This individual product is available for customers who have lost or damaged their existing shims.