Abstract: An instrument for surgical purposes has two relatively movable working parts and two relatively pivotable jaws interconnected in such a way that when they are opened, the two working parts are pushed together, whereby one of the two jaws has a shaft for the pivotable fitting of the other. The shaft is provided with regions of differing diameter and can be axially moved in such a way that selectively a larger or smaller-diameter region is effective in the region of the other jaw, which has a slot for the shaft with a narrower central section and broadened bearing sections at both ends. The width of the slot in the narrower central section lies between the diameter of the two regions of the shaft and has a diameter in the circularly broadened bearing sections corresponding to the larger diameter of the shaft.