Abstract: The nut-runner has a power arm and a reaction arm constructed preferably as a casing, each of which is guided in a first end region so as to be pivotable opposite the other about a common axis. It has a clamp wheel with gearing mounted in a drilled hole in the first end region of the power arm so as to be rotatable about the axis, and a catch mounted on the power arm and interacting with this clamp wheel, said catch being in the engaged position when the power arm pivots in one direction, in which said catch engages with the teeth of the clamp wheel and slips over the teeth of the clamp wheel when the power arm pivots in the other direction. The nut-runner also has a hydraulic power cylinder consisting of a cylinder and a piston and acting between the two arms in the vicinity of their other end regions. The reaction arm encompasses the clamp wheel through a maximum of 180 degrees.

Abstract: The power screw driver has a power arm (2) and a reaction arm (1), as well as a ratchet wheel (7) and a multi-toothed pawl (8), that meshes with this ratchet wheel and that meshes with several teeth of the ratchet wheel (7) when the power arm (2) is in a rotational direction and when it is in the other rotational position, the pawl slips over the teeth of the ratchet wheel (7). Finally a hydraulic power cylinder is provided between the two arms (1, 2).The power arm (2) has a drive head (9), which is inside the cylinder bore hole (11) and engages in a recess (14) of the piston (13). The cylinder bore hole runs obliquely, in particular at a right angle to the power arm (2).