What's the difference between cable tray and metal slot?

First, different prices and sizes. 
It must be that the wire slot is cheap, know why not, because the large size is called the bridge, and the small size is called the wire slot, of course, the large specification requires more materials, it will be more expensive, the specification is small, the materials needed are less, and it will be cheap. 
In fact, metal slots and cable trays are the same, the material can be said to be the same, but the style is different. 
The size is large, that is to say, 600 to 100, it must be a bridge, not a slot. 
In addition: the function is different. 
The bridge is used for laying power cable and control cable, and the wire slot is for laying wire and communication cable; the bridge is relatively large, and it is often used between floors and power distribution rooms of general buildings. 
The wire slot is relatively small; the turning radius of the bridge is relatively large, and most of the line slot is curved at a straight angle; the span of the bridge is relatively large, and the line slot is relatively small; the ways of fixing and installation are different; in some places, the bridge is uncovered, and the wire slot is almost all sealed with a cover. 
Wire slots are often used in distribution cabinets and instrument cabinets. 
So metal grooves are used for walking wires, and bridges are used for walking cables.