You know the question. What is it? There is one in the PGM.
keep spinning
yokaiyo
When a yo-yo has hubstacks, it has three bearings: one for each hubstack and one in the center like a normal bearing. This makes it so you can hold the hubstacks on the side of the yo-yo while the yo-yo is spinning since it has separate bearings. This accounts for some more potential in tricks as well as the ability to pull start. More information in this thread:
(I think that was what you meant.)