Yankee Hill Machine 9630DX: The Yankee Hill Machine Diamond Series forearms feature diamond shaped heat vents, an extended top rail for gap-free installation, \"T\" marked rails to mark accessory locations, accept Yankee Hill Machine end caps, and utilize Yankee Hill Machine anti-rotation screws for secure installation. The forearms and barrel nuts are made of 6061-T6 aluminum and hardcoated to military specifications. The jam nut and anti-rotation screws are steel and plated a matte black finish to match. The assembly includes: one jam nut, one barrel nut, two anti-rotation screws, and one forearm tube. The overall length is 7.29\" and the weight is 12.5 oz.