As the name suggests, the hub blockers have the function of blocking the hub so that it rotates together with the drive shaft, therefore the gears can be shifted with the vehicle lifted inside the box and at the same time using the brakes to stop the rotation.
This allows to warm up the vehicle's engine-transmission inside the box without fitting on the wheels, avoiding the inertia and dangers of the wheels and tyres running load-free with the car lifted, as well as preventing the disc brake from flying out and damage the calliper, which would be loose if the wheel doesn't hold it, minimizing the risk for all the members of the crew inside the box.
The hub blockers are made of high-strength aeronautical aluminium and are available for all racing vehicles with mononut system.