Abstract: A lockable tilting apparatus for the seats of chairs and which can be used selectively either for chairs which tilt backward or for chairs which tilt forward, comprising a base plate securable to chair seat and a stationary body member adapted to be supported by the pedestal of the chair, spring means supported by said stationary body member, means supported by said stationary body member mounting said base plate for tilting pivotal movement relative to said stationary body member, link means engaging and movable with said base plate against the restoring force of said spring means whereby said base plate is tiltably movable relative to said body member against the restoring force of said spring means; and wherein a locking apparatus which is actuatable by displacement of an operating lever between two terminal positions is provided for selectively locking the base plate against tilting movement or for releasing the base plate for tilting movement, characterized by a slide member mounted in said body member f

Abstract: An angle joint, consisting of a ball socket and a ball pivot, is pivotally mounted, by means of the ball, in a ball socket recess which is shaped like a spherical cap and acts as a ball seat. On one side of the ball socket is a rigid locating or contact shoulder, which is integral with the ball socket and partially grips the rear of the ball when the ball has been inserted into the recess.A locking element, which is situated opposite the locating shoulder, also partially grips the rear of the ball when the ball is inserted into the recess. The locking element is slidably located in a guide recess in the ball socket at an acute angle, between 15.degree. to 30.degree., to the direction of insertion. A locking spring presses the locking element in a direction opposite to the direction of insertion. The locking element is loaded by a pretensioned helical spring, acting as a locking spring, which bears both against the locking element and a section in contact with the ball socket.