The Fly Custom Set was a replacement bearing for the YoYoFactory Galaxyfly, a non-responsive yo-yo. It was also an upgrade kit for the Starfly model which used a plastic transaxle bearing and tug response. If the bearing set was used in the Starfly model, you needed to use a substance such as vaseline on the bearing to make the Starfly responsive with a tug.
The set included a full metal UFO bearing which is basically a size A center trac (aka concave) ball bearing axle with metal shims/spacers.
