A spline coupling is composed of parts such as an inner spline ring with the same number of teeth and a flanged half coupling with external teeth. The external teeth are available in two types: straight teeth and drum-shaped teeth. The drum-shaped teeth refer to the external teeth being made into a spherical surface, with the center of the sphere on the gear shaft axis. The side clearance of the teeth is larger than that of general gears. Drum-shaped spline couplings can allow for greater angular displacement (compared to straight teeth couplings), improve the contact conditions of the teeth, enhance the ability to transmit torque, and extend the service life.