To accommodate bulk cargo vessels are often used gripper, whose execution requires special handling of the winch. For the transport of iron blocks and sheets sometimes the cranes are equipped with solenoid, which hold at the start up of the load current by magnetic effects. To operate these magnets are convenient because the striking of the strings, etc. is no longer obtains. The use is always dangerous, because crashes during a power interruption, no matter what cause the load. Therefore, such magnets are only suitable for exclusive material and insensitive to local conditions, the danger for people and valuable material. By security structures of L. piece of wood, weather ob, the use of such magnets, a wide field is opened up: The nature of this device is that the magnet only picking up and setting down of the transported material is left, while on the transport the load lifted is supported by gun design (see illustration).