1The superior 20T worm gear is a better choice of aftermarket replacement for snow thrower. 2The gear is a perfectly replacement for MTD and so on to better meet your demands. 3According to the original factory specifications, replacing reference OE number is 91704861, etc. 4Made of high quality aluminum alloy materials with stable performance and high reliability, have a longer service life. 5Built to stringent OE specifications, design to have the same form, fit and function as OEM original part. Item Type: Worm Gear Material: Aluminum Alloy OEM: 917-04861 / 917-04861-A / 917-0528 / 917-0528A / 717-04449 / 717-0528 Fitment: Replacement for snow thrower Replacement for MTD Replacement for Troy-Bilt 1 xWorm Gear1. Please double check the part number of your item, matching information is for reference only.2. If you are unsure of the item, please contact us before buying to avoid unnecessary return, thanks