The Fan Hub is a component of the engine cooling system found in trucks. It is responsible for driving the fan that helps cool down the engine by pulling air through the radiator. The hub is typically made of heavy-duty materials like cast iron or steel to withstand the high rotational forces generated by the fan blades. It connects to both the engine crankshaft and fan blades using bolts and has a mechanism for adjusting tension on the belt that drives it. If there are issues with overheating, it's important to check the condition of the Fan Hub as it can affect cooling performance if not functioning properly.