Abstract: A micro-adjustable tool chuck comprises a first cylindrical body member (1) adapted for connection to a drive spindle, a second cylindrical body member (2) adapted to receive a tool bit in the end thereof, and moveable axially relative to the first body member (1), and means for drivingly connecting the first body member (1) to the second body member (2). A first screw thread (10) is formed on the outer surface of the first body member (1) and a second screw thread (11) is formed on the outer surface of the second body member (2). The first screw thread (10) is of a greater pitch (coarser) than the second screw thread (11).