These will improve efficiency allowing your track to rotate easier and they are extremely durable. Specify either 20mm (.75") or 25mm (1") shaft. These light weight 9 inch idlers come with a premium 6205 or 6304 Bearing. Larger bearings mean longer life and are stronger. The balls in the bearing are larger and will spin slower compared to a smaller bearing thus creating a longer life expectancy. These will fit Polaris, Yamaha, Arctic Cat, and Ski Doo.