Abstract: This chair height adjustment mechanism has a tubular housing fixed to the chair base, with vertically-spaced bearings providing lateral support for a threaded spindle secured to the chair seat. The upper bearing permits the spindle to move axially, and a nut in threaded engagement with the spindle below the upper bearing is biased upward into clutch engagement with the lower end of this bearing. The biasing spring acts between washers keyed to the spindle, the lower of these being supported by the upper face of the lower spindle bearing. Weight on the seat moves the spindle downward against the spring action to disengage the nut so it can rotate with the spindle, thus removing any change in the height adjustment of the chair when it is occupied.

Abstract: A chair height mechanism in which a threaded nut (30) is threaded onto a threaded spindle (16) and a hub tube (18) supports the spindle through a clutch comprising a locking tube (34) secured to the nut (30) and having lower tapered portion (36), and a cylindrical liner (46) secured to the hub tube and having an upper tapered outer surface (48) which mates with the cylindrical liner (46) inner surface. A compression spring (42) biases the tapered surfaces of the liner (46) and the locking tube (34) into engagement.