Abstract: An hydraulic, bolt tensioning device comprising a reaction component which in use bears against the member from which the bolt shank protrudes, the reaction component having a shank receiving bore extending therethrough, an annular, axially moveable component carried by said reaction component and moveable axially relative thereto by the introduction of hydraulic fluid under pressure between said components, a cam ring secured to said axially moveable component for axial movement therewith, and rotatable relative to said component about the axis thereof, and, a tensioning nut secured to said cam ring for movement therewith, said tensioning nut being divided into at least two relatively displaceable segments moveable relative to said cam ring between an open position in which the shank of a bolt to be tensioned can pass freely between said segments, and an operative position in which the thread portions on said segments mate with the thread of said bolt shank, said cam ring cooperating with said nut segments w