We can see that the pulley is a whole made of iron. And the pulley in front of the crankshaft on the car, many cars in order to reduce the impact vibration caused by engine combustion, cut into two parts inside and outside in the middle ring on the ordinary all-iron pulley, and then bury rubber in the gap between the inside and outside parts. In this way, the power of the engine will be transferred to the inner ring of the pulley, then to the damping rubber of the middle layer, and then from the damping rubber to the outer ring. In this way, the vibration of the engine will be reduced outside the rubber.

To put it bluntly, it's a layer of rubber about five centimeters thick. It can effectively increase the life of the belt. Of course, this rubber layer will also be damaged. If it breaks, the whole belt has to be rotated. However, the life of this thing is much longer than that of the belt.