Abstract: Coupling mechanisms for engaging and releasing a tool attachment such as a socket from a drive element include an engaging element and an actuating element. The actuating element can include a collar or other manually-accessible part, and various features allow for a relatively small outside diameter for the collar or other part. These features include configuring the actuating element to contact the engaging element within the drive element, placing the biasing elements within the drive element, and forming guides for parts of the actuating element within the drive element. Also, the engaging element can move along a direction that is oriented at an oblique angle to the longitudinal axis of the drive element, in whole or in part. The engaging element can have a first part that moves obliquely in the drive element and a second part that moves radially in the drive element to engage the tool attachment.