This Glock Conversion Block is genuinely ingenious and one of the best AR-15 accessories on the market today. This 9mm Glock Conversion Block converts your standard AR-15 lower receiver magazine well to a 9mm Lower, allowing you to use Glock style magazines. This conversion kit is designed to fit into the magazine well of your standard AR-15 and reduces all the extra space and allows Glock 17 and 19 magazines to fit. This is fantastic because it increases the modularity of your standard AR-15 pattern rifle by enabling you to change from 5.56 to 9mm by utilizing this adaptor and merely changing your upper receiver and BCG. This also allows you to purchase standard Mil-Spec lower receivers to build a complete 9mm firearm. This conversion kit is constructed of 6061 aircraft-grade aluminum.