T172543 Spur Gear 57T, 2nd Idler Ring Fits 450J s/n 108452-, 450K s/n F304771-One New Aftermarket Replacement Spur Gear, 2nd Idler Ring (57T) Fits John Deere Crawler Dozers This 57 tooth spur gear serves as the 2nd idler ring in the final drive assembly of Fits John Deere J series and K series crawler dozers. The final drive idler gear train transmits power from the transmission output to the drive sprocket; worn or broken idler ring gears cause loss of drive power and must be replaced to restore full dozer function. This gear