I made a header/exhaust manifold flange for another member and decided to make a couple more for anyone else who might be interested. They are laser cut from 0.5 inch 304 stainless steel (thicker than most competitive flanges). The perimeter design of the head flange is unique and is meant to isolate each runner. This is to prevent warping or buckling of the flange after repeated usage as well as shearing manifold bolts. I also believe that the curves yeild a more attractive finished manifold. Here is a little inspiration for your projects: