The 45 spline spool for 9", 9 1/2" & 10" gear applications was designed to address breakage issues at the bearing journals due inadequate material thickness on extreme duty spools. Some spools center the axle in the center of the spool, this is usually the thinnest section in a spool and most prone to failure. In this spool, the axles are centered at the ring gear mounting plane, the strongest part of the spool. These spools are commonly used in Pro2, Pro4 and prerunner applications. NOTE: The 45 splines in this spool feature a 45 degree pressure angle.