Jon, It's interesting, I've build many coils on 10.75" and 6.625" diameters. They range in size from a few inches tall to 4 foot. But even a short coil 8" or 10" tall and 10.75" diameter makes remarkable sparks, not only long sparks, but THICK sparks. I love large diameter coil forms! Jeff ______________________________________________________ Get Your Private, Free Email at http://www.hotmail-dot-com