The device has a permanent or long-term magnet with at least one lower and one upper covering or with an all-over covering. The covering can be partially or entirely of synthetic material. The side of the magnet facing the upper covering has a handle enabling handling of the device. The handle and the upper covering or coating can be made in one piece. The thickness of the lower covering is between 0.5 and 3 mm., pref. 1 mm.
