This oil seal fits on the PTO output shaft of the host tractor. It prevents lubricant leakage from the transmission housing and blocks dirt and moisture from entering the shaft bearing area. The seal rides on the rotating shaft surface; a worn or hardened lip allows oil to weep past the shaft, which can lead to bearing failure and eventual gear damage. The manufacturer machines the sealing lip to match the original shaft finish and housing bore tolerance, so the seal seats correctly without additional shimming or adapters. On replacement, inspect the shaft surface for scoring and replace the seal if any groove is present.