The invention relates to a mechanical assembly for a power tool, and a power tool incorporating the mechanical assembly. The mechanical assembly includes a first member having a first axis and a first engagement portion inclined relative to the first axis and a second member having a second axis and a second engagement portion inclined relative to the second axis. The first and second engagement portions engage each other by movement of the first and second members relative to each other in the direction of at least one of the axes. The power tool includes a power tool body and a rotatable driven member being operable for releasably gripping a working element, the driven member having a drive mode in which rotation of the driven member drives the working element relative to the power tool body and an adjustment mode in which rotation of the driven member causes the driven member to either grip the working element or release the working element or both. The power tool also includes means for adjusting the driven member between the modes which includes the mechanical assembly wherein the first and second engagement portions engage each other by movement of the first and second members relative to each other in the direction of at least one of the axes and wherein engagement between the first and second engagement portions adjusts the driven member to the adjustment mode and disengagement between the first and second engagement portions adjusts the driven member to the drive mode. The power tool may also include a first torque control means that is operable for controlling the amount of torque applied to the driven member by the power drive when in the drive mode and a second torque control means that is operable for controlling the amount of torque applied to the driven member by the power drive when in the adjustment mode.