Abstract: A height adjustment mechanism for chair backrest or arm comprises a tube-like brace having a transverse elongate groove and transverse apertures; a sliding member in the brace with an upper end secured to backrest or arm; a guide member coupled to a lower end of the sliding member; a hook flexibly coupled to the guide member having an upper bent free end; a first half-cylindrical member in the brace for receiving a portion of the sliding member and the hook, an internal notched member having curved members and a longitudinal channel; a second half-cylindrical member in the brace matingly secured to the first half-cylindrical member, an upper hole, a lower hole, and a spring-depressible detent in the lower hole; and a lock pin inserted through the groove and the upper hole to secure the brace and the second half-cylindrical member together. Backrest or arm may be pushed down to cause the bent end to move through the channel and pulled up to lock in one of the curved members.

Abstract: An adjustment mechanism mounted in a chair for releasably locking one chair component in one of positions relative to a seat. The mechanism comprises a tube-like brace secured to underside of seat; a sliding member slideable in brace secured to one chair component and having lengthwise recesses; a guide member coupled to sliding member; a hook member having a lower end coupled to guide member and an upper bent end; a first member secured in brace including a notched member having curved members and a channel; and a second member secured in brace together with first member for receiving sliding member and hook member, a spring-loaded detent of second member being secured in a hole and having a portion projected from hole into one recess for engagement in an unused state. One chair component is operative to push down to cause bent end to move through channel in response to a disengagement of detent from one recess and pull up to lock in one of curved members with detent engaged with the other recess.