7 Inch Vented Stone Krusher Barrel Extension for AR15 .223/5.56/9mm/.45acp with 1/2X28 threads. Offers a new design and length. For door breach, defense and barrel counterbalance. This machined aluminum vented extension is finished in flat black anodize, 7 inches in length, 1.5" OD and weighs about 15 ounces. Threaded in 1/2x28.