This kit contains two thin size C bearings that together are only 1/3 thicker than a standard size C bearing. In many yo-yos this will give you extra wide gap for even less response. We have only tested these on a few yo-yos, like the YoYoJams, but with the appropriate axle this should fit any size C yo-yo. They also provide the extra bonus of creating a grove between the two bearings that keeps the string centered to prevent the string from rubbing on the sides of the yo-yos. Oh, and 'HI' Doc Pop, thanks for creating Beefcaking.