Machined from 6061 aluminum, we are offering a 13B-REW oil neck flange. It is designed to use the factory oil neck o-ring. No need for the oddly oversized heads of the factory M6 bolts as these holes have been aligned with the mounts. A step has been added for ease of welding on the neck side. Center bore is 29mm and the step is 32.5mm. Each flange will come with a new OEM o-ring and stainless hardware.