What is the sequence between gear transmission and chain transmission?

1. Both ends have joints, one end is used for welding and the other end is used for connection.
2. Single head joint: Only one end has a joint, used for welding and connection.
3. Screw joint: Both ends have threads, one end is used for welding, and the other end is used for connection.
4. Elbow joint: Only one end has an elbow, used for welding and connection.
5. Connection joint: Only one end has a connection, used for welding and connection.
6. Tee joint: All three ends have joints, used for welding and connection.