Chair seat sliding and locking mechanism

A chair seat sliding and locking mechanism comprising:

• a positioning tube configured to be mounted to a rod of a base of a chair having a chair seat, wherein the positioning tube is rotatable relative to the rod but is not slidable relative to the rod along a longitudinal axis of the rod, and wherein the positioning tube includes a positioning portion;
• a sliding seat including a coupling portion coupled with the chair seat, permitting joint movement of the sliding seat and the chair seat, wherein the coupling portion includes a receiving portion having a receiving hole with a catching portion, wherein the positioning tube is received in the receiving hole, wherein when the positioning tube is rotated relative to the rod to a first position in which the positioning portion disengages from the catching portion, the sliding seat is movable along the positioning tube, and wherein when the positioning tube is rotated relative to the rod to a second position in which the positioning portion engages with the catching portion, the sliding seat is fixed relative to the positioning tube.