Tuned pipes have a brass ferrule silver soldered to the head pipe. The stepped header that is bolted to the engine has a seat machined on its inner rear edge that matches the ferrules radius. The round knurled clamp nut has the same radius machined on its inner rear edge. When the two are screwed together there is no leakage. A small amount of movement is allowed because the stepped area in the engine header piece is .015 larger in dia. than the head pipe. Pipe pressure is picked up between the engine & the stepped header. This system completely eliminates silicon rubber "O" rings & tubings used to seal & connect tuned pipes to engines.
