Abstract: An ignition coil for a spark ignition engine generally includes primary and secondary windings disposed about a magnetic core. The secondary winding is wound around a spool. The spool includes a cylindrical body having opposite first and second ends and a winding section between the ends. A conical winding surface at one of the ends tapers from a large diameter at the one end to a smaller diameter. A grooved surface extends axially toward another of the ends of the body and extends to adjacent the smaller diameter of the conical surface. The grooved surface contains longitudinally spaced continuous circular grooves that have unequally angled sides. The sides toward the one end are sloped at a greater angle relative to a radial direction than are the sides toward the other end. The secondary winding is wound around the winding section forming a plurality of turns of wire wound one over the other at a desired angle. The grooves are sized such that only one turn of the wire is disposed within each groove.