Yankee Hill Machine Co A3 Upper Receiver, Fits AR15, 7075-T6 Aluminum, Anodized Finish, Black YHM-100 YHM has long been a manufacturer of quality AR-15 Upper Receivers and is very proud to offer their A3 Upper Receivers. These uppers were designed" and are MACHINED 100% IN HOUSE by YHM and are forged from 7075-T6 aluminum. Fit and function with your standard lower receiver.