An improved shuck has one end coupling with a fabrication machine through a holding member. The chuck includes a coupling structure, a grip means and a shank. The coupling structure has a first screwing portion at one end and a fastening member at the other end. The grip means has a second screwing portion at one end engageable with the first screwing portion and a plurality of grip jaws at the other end inclined outwards. The coupling structure and the grip means are held in a through hole formed in the shank. The through hole has an internal side to form compact holding of the grip means to firmly hold a tool. After the coupling structure is anchored through the fastening member, the shank can be turned to drive the grip means to move, and the grip jaws can be expanded or contracted to release or grip the tool.