Just the fact that the S&S® polished billet rocker covers for shovelhead engines look so good may be reason enough to put them on your bike, but the beauty is not just skin deep. The well thought out design offers a number of advantages over conventional cast rocker boxes. Machined from billets of 6061-T-6511 aluminum on modern CNC machining centers, these rocker boxes provide the ultimate in dimensional accuracy and stability. The top and bottom sections of the covers are sealed with an o-ring type seal that insures leak free operation. Rocker shafts used in the S&S® rocker boxes are a strong and economical straight design. Anyone who has had to replace a set of stock shovelhead rocker shafts can tell you that this will save you money when it comes time to rebuild the top end.