An adjustment mechanism for a lifting device includes a longitudinal clamp bar and a clamp slidably disposed on the clamp bar. The clamp has a clamp body and at least one clamping member movably connected to the clamp body. The at least one clamping member is operative for (1) acquiring a clamped condition when a lifting force is applied to the clamp body, wherein in the clamped condition, the at least one clamping member is engaged with the longitudinal clamp bar to prevent movement of the clamp along the clamp bar and (2) acquiring an unclamped condition when a lifting force is released from the clamp body, wherein in the unclamped condition, the clamp is free to move along the clamp bar.