The Yankee Hill Diamond Series Forearm is an excellent way to upgrade your AR-15 with one of the best forearms available. This is a durable 6061-T6 Aluminum forearm that comes with 4 rails, and the top rail is extended for a gap free fit. The design is meant to dissipate heat quicker than their competitors with their innovative Diamond Cutouts. If you want the best, the Yankee Hill Machine AR-15 Diamond Series Forearm is an absolute contender.