Abstract: A chuck assembly includes a hollow chuck body assembly, a jaw unit provided at a lower end of the chuck body assembly, and a rotary shaft disposed in the chuck body assembly and coupled with the jaw unit. The chuck body assembly has a top surface formed with first annularly arranged ratchet teeth. The rotary shaft has an upper end portion extending outwardly from an upper end of the chuck body assembly. A sleeve member is sleeved on the chuck body assembly. A rotary ring is sleeved on the upper end portion of the rotary shaft and has a bottom surface formed with second annularly arranged ratchet teeth which engage normally the first ratchet teeth so as to restrict undesired rotation of the rotary shaft in the counterclockwise direction. A rotary knob is sleeved on the sleeve member and is coupled with the upper end portion of the rotary shaft.