The wheels automatically loaded in the workposition and is centered by two groups of lateral flanges which press all around the circunference of the rim. At this point, the four screwing heads intercept the nipples one by one and tighten them until the presetted required tension. The screwing operation alternates with the rotation of the entire wheel-blocking group. The correct tightening tension is obtained by programming the torch of the screwing motors. After all the spokes have been secured, the flange group opens and the wheel is automatically expelled to accept the next wheel.