Our New Vented Stone Krusher Flat Spiked extension for the AR15 threaded in 1/2x28 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 and weighs about 10 ounces. May Be used to reach compliant barrel length if pinned and welded. Be certain to check your barrel length.