expansion head for expansion tools for hollow workpieces , particularly for the ends of plastic pipes and metal - plastic composite pipes , comprising a union cap with a radially inwardly oriented guide flange , and a set of sector - shaped expandable jaws , each of which is individually received in the union cap in a radially movable manner by an inner flange sector that overlaps with the guide flange , the set of sector - shaped expandable jaws being movable between a closed state and an expansion state , and an approximately cylindrical lateral surface being embodied in the closed state by the outer wall of the expandable jaws , wherein the outer wall has at least one recess and / or raised area extending in the direction of the longitudinal axis of the expandable jaws .