A chair control is shown for adjusting the horizontal position of a chair armrest or a chair back. A support bar, upon which the chair armrest or back is mounted, a slidably located in a mounting bracket usually attached to the underside of the chair seat. The mounting bracket includes a first pivot pin spaced transversely of the support bar, and a rigid lever mounted on this pivot pin, the pivot pin acting as a fulcrum. The rigid lever includes a first end portion that pivots into locking engagement with the support bar and a second remote end portion. An over-the-centre toggle linkage is coupled to the lever second end portion to rotate the lever about the pivot pin to engage the support bar and lock it in position.