Abstract: A vertically and rotatably adjustable chair arm assembly is secured to a support tube mounted to a chair seat. The chair arm assembly includes a lower outer shell and a plastic sleeve received within an axial bore of the outer shell. A plastic collet is concentrically positioned within the sleeve. The plastic collet includes upstanding positioning tabs adapted for engagement with longitudinally extending alignment grooves formed on the interior surface of the sleeve. The chair arm assembly is secured on the support tube by sliding the sleeve and outer shell slide over the outer surface of the support tube. The plastic collet extends into the upper end of the support tube so that the metal support tube surface is sandwiched between the plastic sleeve and the plastic collet. A lock mechanism having a locking arm telescopically positioned within the plastic collet is pivotally connected to the outer shell.