A lockable articulation for permitting relative angular rotation between a first and a second part, such for example as the body of a three-wheeled vehicle and the rear axle of the vehicle, said articulation comprising a hollow cylindrical drum centered and mounted on one part, e.g. the axle, two cylindrical sector-shaped jaws arranged inside the drum for contacting the inner surface of the drum and with their ends facing each other, at least two facing ends defining dihedral surfaces whose angle is outwardly opening, and means coupled to the other part, e.g. the vehicle body, for spreading the jaws apart into frictional engagement with the drum to lock the other part against rotation relative to the one part, said means including a roller interposed between the drum wall and the dihedral surface of the jaws and a knee lever having two-pivotally connected links one of which is pivotted on the other part and the other of which rotatably supports the roller.