This special deep groove ball bearing 638-2Z is used on many scooters (e.g. CPI, Keeway and Piaggio) as a support bearing for the gear shaft in the vario cover.
Inner diameter: 8mm
Outer diameter: 28mm
Thickness/Depth: 9mm
OEM numbers for comparison: 82521R, 4016021, A011023, 756.00.82AI-translation