The heavyweight class Butterfly with the hubcap design.
The wheels have been around for decades. With a wide gap for a design of its age, and a heavy weight to top it off. This fixed axle model has a reasonably long sleep, considering its construction, making brain twisters and split the atoms relatively easy.
In 2000, the wheels was modified by some fanatics to include metal ball bearings, which made it substantially easier to handle and throw difficult tricks. This mod gained extreme popularity, and is said to have been used to design the original Freehand. You could say that the Wheels is the true originator of modern string play, and you probably wouldn't find many to argue that. Wheels was the model that changed yo-yo history, and is still given much respect from Duncan Crew Members and core players alike. Once you try it for yourself, you'll understand why. The wheels, they keep turning.
This is a fixed axle yo-yo
This is a responsive yo-yo