This is a replacement Wheel Bearing for the Pro-Lift Automatic, Pro-Dolly™ HD2 and Pro-Dolly™ HD1 wheels. It is made from machined steel and hardened so it can handle harsher abuse.
The Wheel Bearings may need to be replaced if they are damaged by overloading or shock loads (such as a piece of stone dropped on it, or the dolly tossed onto the ground).
We don't see this very often, but when we do, it is usually caused by a dolly that overloaded at one time (causing the initial damage) and then continued use overtime causes further damage.
Please be sure not to overload the Pro-Lift or Pro-Dolly™, and always inspect it for issues prior to use.