Abstract: A chair back support arrangement of a type including an upright supporting a back support arranged to slidably engage the upright, and interlocking means to maintain a selected support height for the back support, the interlocking means including a rack either affixed to or being part of the upright an engaging member supported by the back support and arranged to selectively interlock with the rack and being able to be activated to effect a change from interlocking to not interlocking by a change by relative positioning of the back support with respect to the upright. A catch is supported by the support back so that in one position, it can catch and hold in a non-engaging position, the engaging member clear of the rack, and in another position, it will release such engaging member to effect an interengaging action with the rack.