CNC machined billet neck. Ideal for use wherever a heavy duty filler neck is required. Accepts standard Stant style caps.Heavy-duty filler necks are perfect for custom applications. They feature 6061-T6 billet aluminium construction for durability in racing or street applications. These fill necks include 1/8" NPT to 5/16" (8mm) barbed fittings for the plumbing of an expansion tank.The neck measure 58mm OD at the base, 56mm at the top, and is 25mm deep, the base is 5mm thick. The internal hole closest to the radiator is 29mm.