A rock bolt comprising a shaft having first and second ends, and an anchoring device operative to retain the bolt when located in a drilled hole and comprising a mandrel mounted to, or integrally formed with, the shaft and at least one expansion element overlaying the mandrel, at least one of the mandrel or the at least one expansion element being a movable member and being able to rotate relative to, and move axially along, the shaft, the at least one expansion element being arranged to be displaced radially outwardly on a predetermined relative movement between the mandrel and the at least one expansion element, wherein when disposed on a first portion of the shaft, rotation of the movable member relative to the shaft causes axial movement of that member along the shaft, and when disposed on a second portion of the shaft, the movable member is able to rotate on the shaft without being biased to move axially along the shaft.