a locking mechanism suitable for use with office type chairs comprising an operating lever movable between a locking position in which locking takes place and an unlocking position in which unlocking takes place , a spring , which biases the lever into the locking position and a catch , which holds the lever in the unlocking position upon movement of the lever into the unlocking position . the catch is disengaged when the lever moves past the unlocking position . upon disengagement of the catch , the lever returns to the locking position under the action of the spring .