Locking device for mutually pivotable members

A device (1) for locking two mutually pivotable members such as the back and seat of a chair, in any of a plurality of positions comprises a ball member (6); a first element (2) for connection to one of said members; a second element (3), for connection to the other of said members and having a through hole, in which the ball member is located, and a third element (4) for rotation with respect to said second element between two positions in one of which (Fig. 1B) the first and second elements are able to pivot while in the other position (Fig. 1A) the ball member (6) is lockingly engaged by both the first element and the third element. The embodiment shown has flat elements engaging (at 7, 8) the pivot axis of the members. The element (2) has a plurality of recesses while the element (4) has a recess adjoining a shallower channel. The elements (3, 4) may alternatively have a curved slot and channel respectively. In a further embodiment the three elements are formed as coaxial cylindrical members.