Abstract: The wrench is for use with a bolt having an axial bore in which is located a pin. The pin is rotatable within the bore until the bolt is tensioned near its elastic limit, at which point rotation of the pin relative to the bolt is restrained.The wrench includes a body (12) drivingly carrying via dogs (20) a first socket (16) for engaging and driving a nut on the bolt. A second socket (28) engages a head on the pin. The first and second sockets (16,28) are connected to a common drive, the connection of the second socket (28) being in a coupling in which a pin (46) engages in a detent in a cam cylinder (50).When rotation of the pin relative to the bolt becomes restrain bed, the coupling (46,50) disengages, allowing the cam cylinder (50) to be urged outwardly of the housing (12) by a spring (60), to cause a warning indicator (58) to be displayed.