Abstract: A chuck for a drill head of a rotation rock drilling rig, wherein a plurality of jaws are equally angularly distributed around a grip position axis, wherein the jaws co-operate with actuator means for radial movements of the jaws, and wherein the chuck includes urging means being arranged for influencing the jaws into the release position. The urging means is a partially annular jaw spring surrounding said axis and having two spring ends adjacent to each other. The jaws together form an inside seat for the jaw spring and the jaw spring is arranged for fixing engagement with one of the jaws. The invention also relates to a drill head, a rig and a jaw spring.