A chuck includes a driving element, a sleeve movably installed on the driving element and a ring fit in the socket. The driving element includes a socket for receiving a bit, a shank extended from and a shoulder formed between the socket and the shank. The sleeve includes a shoulder formed on an internal side for contact with the shoulder of the driving element for avoiding detachment thereof from the driving element in a direction. The restraint is fit in the socket for avoiding detachment of the sleeve from the driving element in an opposite direction.