For RZ Series: 2019-2020 RZ, 2019-2020 RZ Pro, 2020 RZ HD. Part Number: 437-0004-00, 437000400 mower spindle for Spartan 72″-Deck mowers. For SRT Series: 2017-2019 SRT, 2020-2021 SRT Pro, 2020-2021 SRT HD, 2019-2022 SRT XD.