A chuck has a chuck body adapted to be rotated about a chuck axis and formed with a plurality of axially forwardly open passages each having a pair of angularly confronting side faces, respective guides pivotal in the passages about respective guide axes extending secantally of the chuck axis, and respective elongated jaw arms axially slidable in the guides. Each jaw arm has a pair of oppositely angularly directed side faces angularly confronting and spaced from the respective passage side faces. Two guide plate in each of the passages each have an outer face engaging one of the respective passage side faces and an inner face engaging the respective arm side face. These plates are releasably fixed in the chuck body.