enable large diameter bolts to be tensioned with ease to high and accurate preloads. A hydraulic pump activates the internal jacking system, so the effort required to tighten a very large diameter bolt is reduced to the effort needed to operate the pump. As there is no nut rotation during tightening, the operation can be performed in a confined space and torsional stresses on thread damage are eliminated. Any number of hydraulic nuts can be connected together for simultaneous operation, ensuring all bolts in the joint can be evenly loaded to the same high and accurate preload.