Roomba 500, 600 series side brush gear. Usually these gears don't fail, the intermediate gear does, but often the screw to retain the brush strips. Printed in PLA. Some filing of the hex may be required for the brush to fit. Slowly cut the threads for the brush screw, with the brush screw quarter turn at a time then back out until the screw fully seats. The small spacer is placed on the shaft first then the gear, it made printing simpler
Redesigned gear to incorporate the spacer and gear as a one piece unit. Printing this will require rafts and supports. File added as Roomba side brush gear 2 v4. Also added some draft to the hex portion for better brush fitment.