A wrench comprises a handle portion, a head portion releasably secured to the handle portion and a release device. The head portion has an inner surface that defines a fastener receiving aperture and a side entry to the fastener receiving aperture and is movable relative to the handle portion between a loading position in which the side entry is open and an operating position in which the side entry is closed. The head portion is operable to close around a fastener received in the fastener receiving aperture in response to a torque applied in a predetermined direction using the handle portion. The release device is arranged to at least assist in releasing the head portion from the handle portion to permit the head portion to be separated from the handle portion.