Slip-proof clamping system

A slip-proof system comprising:

• a screw connection element having recesses and a wrench with cams which fit into the recesses,
• the screw connection element has an axis, a cylindrical lateral surface and a ring-shaped end face,
• the recesses extend axially parallel from the end face over at least a portion of the lateral surface,
• a radial extension of the recesses being restricted to a part of the wall thickness of the screw connection element,
• the recesses having opposing side walls, the side walls confining the recesses in angular direction and having an outer area and an inner area, and a base extending in angular direction between the side walls and confining the recess in axial direction opposite the ring-shaped end face,
• the side walls being flat and defined by planes containing the axis in the outer area extending from the end face to about half of the axial length of the recesses,
• the recesses being expanded by oppositely situated semicircular protrusions of the side walls in the inner area adjoining the outer area of the side walls, and
• the wrench has a head which is provided with cams which in the axial direction are insertable into the recesses.