The specifications of V-belts are divided by the dimensions of back width (top width) and height (thickness). According to different dimensions of back width (top width) and height (thickness), V-belts of different standards have different models. The pitch width, top width and height of V-belts of each model are different, so the pulley must also make various groove types according to the shape of V-belts; These different groove types determine various types of pulley.