Overhead crane can work above the rectangular ground, mostly it is used to load and unload objects in the warehouse, workshop and open storage area. It can be divided into two groups as below.
(1) Beam crane. Beam crane mainly includes bridge type single beam crane and bridge type double beam crane. Main beam for single beam crane is mainly compound section combined by joist steel/structural steel and steel plate. Lifting trolley is usually assembled by chain block, electric hoist or hoist as lifting mechanism parts. 
Beam crane has two types: bridge support type and hanging type. The crane span structure of the former moves along crane rail on the beam; that of the latter moves along the rail hanging below the workshop roof.
Bridge type single beam crane can be operated by hand and electricity. 
1. Hand operated bridge type single beam crane
a. Hand operated bridge type single beam crane has a lower working speed, smaller lifting capacity. With a light self weight, it is convenient to organize production and features low cost. It is suitable for occasions where there is a low demand on speed and productivity and where there is less carrying work without power supply.
b. Hand operated bridge type single beam crane uses manual-operation monorail trolley as the moving trolley, chain block as lifting mechanism. The crane span structure is made up of main beam and end beam. Usually main beam is one joist steel, while the end beam is welded by structural steel or bending forming steel plate.
2. Electric bridge type single beam crane has a higher work speed and productivity and a larger lifting capacity. The crane is made up of crane span structure, crane travelling mechanism, electric hoist and electrical parts.
(2) Bridge crane
Bridge crane moves on elevated rail, also called overhead travelling crane. Its crane span structure moves longitudinally along elevated rails at two sides, lifting trolley moves transversely along rails mounted on the crane span structure, which forms a rectangular work range, thus can make full use of space below the crane span structure to lift materials but get out of obstacles from ground equipments. Bridge crane is widely used in warehouse indoor and outdoor, workshop, wharf, open storage yard and other places.
Bridge crane can be divided into three kinds: general purpose bridge crane, simple girder bridge crane and bridge crane for metallurgy purpose. Usually general purpose bridge crane is made up of lifting trolley, crane moving mechanism and crane steel structure. 
The lifting trolley includes lifting mechanism, trolley moving mechanism and trolley frame. Lifting mechanism is made up of motor, brake, reducer, drum and pulley block. Motor reducer drives drum to rotate, then the steel wire rope rolls on the drum or rolls down, thus lift the objects. The trolley frame is usually of welded structure, is the rack of support, installation lifting mechanism and trolley moving mechanism.