The shaft butt diameter is the outside dimension of the end portion of the shaft on the side it is mounted on and is measured in inches. If the piston diameter and size are the same numbers, the thickness will be the standard size. The thick product suppresses wrist tension and reduces the chance of the face surface wobbling. Since it is difficult to apply additional force to the grasping hand, the striking speed increases, thereby improving direction. Plus, the club feels light.