Free wheel hubs, also known as locking hubs or manual hubs, serve a specific purpose in the four-wheel-drive (4WD) or all-wheel-drive (AWD) systems of vehicles. The primary purpose of free wheel hubs is to allow the front wheels to rotate freely from the front axle shaft when the 4WD system is not engaged. Here are the main purposes and functionalities of free wheel hubs:

1. **Disengagement of Front Wheels:** The free wheel hubs allow the front wheels to be disconnected from the front axle shaft. When the hubs are in the "free" or "unlocked" position, the front wheels can spin independently of the front drivetrain components.

2. **Reduced Drivetrain Resistance:** By disengaging the front wheels, free wheel hubs reduce the mechanical resistance in the front drivetrain. This can result in improved fuel efficiency when the vehicle is operated in two-wheel-drive (2WD) mode, as there is less rotational resistance from the front differential, axle shafts, and front drivetrain components.

3. **Extended Component Lifespan:** When the 4WD system is not engaged, having free wheel hubs in the "free" position reduces wear and tear on the front drivetrain components. This can contribute to an extended lifespan for components such as the front axle shafts, U-joints, and differential gears.

4. **Easier Maneuvering:** With the free wheel hubs in the "free" position, the front wheels can rotate freely, making it easier to maneuver the vehicle when 4WD is not required. This can be advantageous when driving on paved surfaces or in situations where maximum traction from all four wheels is not necessary.

5. **Reduced Wear on Front Tires:** When the 4WD system is not engaged, the ability to disconnect the front wheels through free wheel hubs helps reduce tire wear on the front tires. This is because the front tires do not have to rotate the front drivetrain components, resulting in less mechanical resistance and tire wear.

6. **Enhanced Fuel Efficiency:** The reduced resistance in the front drivetrain when the front wheels are disengaged can contribute to improved fuel efficiency. This is particularly noticeable when driving in 2WD mode for extended periods.

It's important to note that free wheel hubs are typically found in older or traditional 4WD systems, especially in vehicles with part-time 4WD. Many modern 4WD and AWD systems use automatic locking hubs or full-time AWD systems that do not require manual engagement or disengagement of the front wheels. The specific functionality and design of free wheel hubs may vary between vehicle models and manufacturers.