YoYoFactory CBC Size XS (Size K / Mighty Flea) Professional Yo-Yo with High-Speed Bearing - Perfect for Beginners, Trick Practice & Competitive Play

This is the Size XS (aka Size K) bearing used in YoYoFactory yoyos such as the Mighty Flea and Loop 360/720 yoyos, Yomega Raider, etc.  It may also be used by other yoyos.

The size of the bearing is as follows:

• Outer Diameter - 8mm
• Inner Diameter - 4mm
• Width - 3mm

Before buying this bearing make sure it will fit your yoyo, as it is not commonly used.  Most yoyos these days use the standard Size C bearing.