YoYoFactory made bearings for your YoYoFactory yo-yos (will also fit many other model of yo-yo)
Size C (6.35 x 12.7 x 4.7498mm)- suitable for the majority of yo-yo factory yo-yos (and most yo-yos in general) as size C is now the industry standard for yo-yo bearing size.
Half Spec - these are half the width of a standard C bearing, and are used in all YYF responsive yo-yos.
Small (5x10x4mm)- Designed for small bearing yo-yos such as the FAST 201 and Velocity