A
power tool for fastening objects has a housing with a non-rotatable element, a power drive in the housing and provided with a rotatable driving element, and a
fastener part including a bolt having a thread and an axis and introducable into parts forming an object, a nut screwable on the bolt and cooperating with the rotatable driving element, and a
washer to be applied between the nut and an object and cooperating with the non-rotatable element, the
washer having an axis and being provided with a first bearing face surface located at one axial side and adapted to cooperate with the nut, a second bearing face surface located at an opposite axial side and adapted to cooperate with the object, and at least one third turning resistant surface adapted to cooperate with the thread of the bolt, so that when driving element turns the nut with a given
active force in one direction and the
washer is held stationarily applied by the non-rotatable element of the housing, the nut turns to tighten or loosen the bolt, and the washer remains rotation stationary while the bolt elongates or relaxes in an axial direction.