Back support means

Claim 1

A back support mechanism for a backrest of a chair mountable between two spaced side rails of a chair, said mechanism including: adjustable support means including laterally disposed link members, each said link member having an upper and a lower arm, said support means further including two guide posts, said arms of each said link member engaging with a respective said guide post at spaced locations therealong, said arms being formed on an end portion of each said link member, each said link member having meshing projections formed thereon and spaced from said arms such that said meshing projections of said link members engage during operation of the mechanism; a bearing pad means pivotally secured to said link members adjacent said meshing projections and bridging between said link members; a pair of spaced guide rails extending between the side rails of the chair, said guide posts being mounted for movement along the guide rails; and, control means including a screw threaded shaft engaging said guide posts such that rotation of said shaft in one direction causes said guide posts to move towards one another and thereby cause the meshing projections to mesh and move the bearing pad means to an extended position and rotation of said shaft in a direction opposite to said one direction causes said meshing projections to mesh and said bearing pad means to move to a retracted position.