Tamiya 9mm Ball Bearings (2pcs.)(15344)

A pair of 9mm outer-diameter ball bearings for Mini 4WD rollers, sold as Grade-Up Parts No.344. Swapping a kit's stock plastic roller bushing for a sealed ball bearing lets the roller spin with far less friction as it brushes against course guardrails, helping the car hold its speed through corners and reducing wear on both roller and rail over a race.

• Outer diameter: 9mm
• Thickness: 3mm
• Quantity: 2 ball bearings
• Includes 4 brass bushings and screws for mounting

Ball bearings are the standard first upgrade over the kit's stock plastic roller bushing: a bushing slides directly against its shaft and gradually wears and stiffens over a race, while a bearing's rolling resistance stays close to constant. At 9mm outer diameter and 3mm thick, this is the smaller of Tamiya's two everyday roller-bearing sizes -- the 11mm, 4mm-thick version (Grade-Up Parts No.345) suits larger-diameter rollers needing a wider bore. The four included brass bushings double as axle sleeves, so no separate axle purchase is needed to fit them.