Abstract: A method and apparatus for tensioning groups of studs to a predetermined strain. The method includes the steps of tensioning all of the studs simultaneously to a predetermined tension, tightening working nuts, releasing the tension on the studs, measuring the residual strain on the studs and determining for which studs the strain is outside a predetermined tolerance range, retensioning the studs to a tension greater than the predetermined tension, rotating the nuts for the studs which are outside the predetermined residual strain tolerance range in step by amounts and in directions corresponding to the amount and direction in which the strain deviates from the predetemined value and releasing the tension on the studs.

Abstract: A hydraulic nut or washer or bolt head comprises piston means let into the recessed end-face of a body. Means for applying hydraulic pressure to a chamber or chambers behind the body are provided to urge the piston means in a direction which leads out of the end face. The piston means has an overall dimension in a first transverse direction which is less than the least possible overall dimension of an annular piston giving the same piston face area and having an overall dimension in another transverse direction, at right angles to the first, which is less than the least overall major dimension for a pair of opposed circular pistons giving the same piston face area. A sealing member comprising a layer of moulded deformable substantially incompressible material on a former is provided in the chamber to contain the hydraulic fluid.