MW 12" aluminum 40 spline spools are produced from 7075 alloy forgings and are finished with a chromate conversion coating. The bearing journals and ring gear flanges are CNC ground on special fixtures that ensure perfect concentricity with the axle spline and near zero ring run-out. 53104 spool is for use with a 3.125" mounting distance (pinion center to ring gear surface), 3.89 - 5.83 gear ratios. Installation - Service instructions can be found on Service Bulletin #0046.