Various work-saving means of conveyance can be used to efficiently move products in the warehouse as well as to store and retrieve products. On one hand, these means of conveyance include permanently installed systems such as overhead conveyor systems Overhead conveyor system , cranes [cran], wheel conveyors [Wheel conveyor] and electric trolley conveyors [Electric trolley conveyor]. On the other hand, they encompass such unattached means of conveyance as forklift trucks Forklift truck , forklifts Forklift and automatic-guided transport systems [Automatic-guided transport system]. Special storage and retrieval equipment is also available. It simplifies warehousing and retrieval in things like pallet-rack, high-bay-rack or tank-rack storage.