This gear wheel transmits drive from the threshing mechanism input to the cylinder or rotor shaft. It is mounted in the gear train that synchronizes the threshing drum speed with the feed and separation systems. A worn or damaged gear tooth causes slipping or irregular drum speed, which reduces threshing efficiency and can overload the drive belt or clutch. The original gear geometry matches the mating pinion’s tooth profile and center distance, so no shimming or backlash adjustment is required during replacement. On reinstall, verify the key and keyway are free of burrs and torque the retaining nut to specification.