A height adjustment system for a desk, workstation or the like is provided comprising a plurality of height adjustable legs each having a first part in the form of a hollow column and a second part movable relative to the first part in a vertical direction. The second part of each leg includes a gearbox housing containing a crown gear provided on a vertically extending rotatable shaft and at least one pinion gear engageable with said crown gear. The vertical shaft includes a screw-threaded portion engaged by nuts on a base plate of the column. A winding mechanism is provided for rotating a horizontally extending shaft on which the pinion gear is provided. Rotation of the horizontal shaft causes the vertical shaft to rotate thereby moving the second part relative to the column so adjust the height of a top member secured on the gearbox housing. The gearbox housing includes ball bearing race assemblies for the crown and pinion gears which enable the height or two or more legs to be adjusted simultaneously by a single winding mechanism. The leg also includes a self-adjusting linear bearing between telescopically movable parts of the leg.