Coupling unit

The coupling unit (10) has two coupling sub-units (10A,10B) that are joined together. Each sub-unit is connected with one of the portions of a jaw section (12) and one of the portions of a hinge pin section (16). The portions of the jaw section, the portions of casing section (14), and the portions of the hinge pin section are integrated with each other. The sub-units are made from steel or iron.