Chuck assembly

A chuck assembly in which a rotary sleeve (2) provided on a body (1) is rotated, jaws (4) engaged with an annular assembly of divided nut elements (3) are moved back and forth to be opened and closed by the rotation of the divided nut elements (3) rotated together with the rotary sleeve (2) and a tool is clamped by the jaws (4), whereby a ring member (8) is provided around the divided nut elements (3), a linear projection (10) is provided on the ring (8), which engages with a groove (9) comprising a circumferential portion (9a) formed on the sleeve (2) to prevent the ring (8) and the sleeve (2) from falling apart from each other. The sleeve (2) further comprises a groove (6) having a greater width than that of the linear projection (10) extending from the end of the sleeve remote from the jaws to the vicinity of the circumferential groove (9) with a tapered surface (6a) at the end nearest the jaws that is formed so as to widen in the direction away from the jaws (4).