Sylvan Arms GCB100: This fantastic conversion kit from Sylvan Arms is one of the best accessories on the market today and increases the modularity of your AR-15 pattern rifle. This 9mm Glock Conversion Block converts your standard AR-15 lower receiver magazine well to a 9mm Lower using Glock magazines. The fit and function of this adaptor are exceptional. All Sylvan Arms products feature a limited lifetime warranty and are proudly designed, built, and assembled in the USA!