At less than an ounce, this AR-15 bayonet barrel adapter is very lightweight, and fits standard 3/4a ^2 barrels with 1/2-28 threads, such as the S&W M&P15 in .223/5.56. It is also easy to put on. Just remove your flash hider and crush washer, slip on the adapter and add a new crush washer, and then screw on your flash hider or other muzzle device. Bayonets that will work include: M7 bayonet M9&nbs