A screw actuated press unit for mounting parts with press fit includes a casing, an actuating screw rotationally journalled in the casing and coupled to a rotation motor, a nut assembly cooperating with the actuating screw, a thrust rod rigidly connected to the nut assembly and extending out of the casing for connection to a work piece, and a locking device effective to rotationally lock the nut assembly to the casing at rotation of the actuation screw, wherein the lock device includes at least three roller studs mounted on and radially extending from the nut assembly and arranged to guidingly cooperate with two parallel guide rails at the edges of an axially extending slot in the casing. The roller studs are spring biased in opposite directions in contact with the guide rails so as to eliminate rotational play between the nut assembly and the casing.