This gear set transfers power from the threshing drum to the downstream beater and straw-walker drives. It is located in the threshing drive housing, where its tooth geometry and mesh clearance determine the rotational timing between the drum and the separating elements. A worn or incorrectly meshed gear set introduces backlash that causes uneven drum speed under load and accelerates bearing wear on the adjacent shafts. The original manufacturer machines the tooth profile and bore tolerances to match the housing's center distance, so no shimming or selective fit is needed during replacement. On installation, verify that the keyway aligns with the shaft key and that the retaining hardware is torqued to specification.