Abstract: A split nut assembly for use in hydraulic tensioning of bolts and studs comprising, first and second nut halves, guide means for guiding movement of the nut halves relative to one another between a closed position in which the nut halves define a screw-threaded bore in use receiving the shank of a bolt to be tensioned, and an open position in which the nut halves are spaced from one another to allow the nut to be moved axially relative to a bolt shank in use, resilient means urging the nut halves to their open position, and an over-centre type linkage pivotally connected at its opposite ends to the nut halves respectively, said linkage comprising a first link pivotally connected to said first nut half for movement about a pivot axis, and a second link pivotally connected to said second nut half for movement about a second pivot axis, said first and second links being pivotally interconnected for movement about a third pivot axis parallel to and spaced from said first and second pivot axes, said linkage having