The roll consists of a roll body, a roll neck and a shaft head. The roll neck is installed in the bearing and passes the rolling force to the frame through the bearing seat and the press-down device. The shaft head is connected to the coupling to transfer the rolling torque. There are three main types of shaft head: plum shaft head, universal shaft head, keyway or cylindrical shaft head. Practice has proved that the shaft head with double keyway is easy to crack in the practical process, and the shaft head with platform is commonly used to replace the shaft head with double keyway at present.