What do the letters in the bridge specification and model table represent?

The letters in the bridge specification and model table represent the specifications and types of the bridge. Usually, a bridge refers to a metal or plastic conduit used to carry objects such as wires and cables.  

The specifications of cable trays are usually represented by their width and height. For example, a bridge with a specification of "200mm x 100mm" indicates a width of 200mm and a height of 100mm. In addition, the specifications of the bridge frame may also include parameters such as wall thickness and bending radius. In addition, there are different ways to represent the types of cable trays.

Some common types of cable trays include:

1. Ordinary bridge frame: also known as plate bridge frame, is a common type of bridge frame mainly used for laying wires, cables and other objects.  

2. Trough type cable tray: also known as trench type cable tray, is a type of cable tray with strong load-bearing capacity, usually used for laying large cables or pipelines.  

3. Tray type cable tray: also known as trough type cable tray, is a type of cable tray with strong load-bearing capacity, usually used for laying large cables or pipelines.  

4. Closed bridge frame: also known as closed bridge frame, it is a common type of bridge frame mainly used for laying wires, cables and other objects.  

5. Fiberglass cable tray: also known as fiberglass trough cable tray, is a type of cable tray with high strength and anti-corrosion performance, usually used for pipeline laying in humid or corrosive environments.  

In short, the letters in the bridge specification and model table usually represent the specifications and types of the bridge, which are used to help people better choose and use different types of bridges to lay wires, cables, and other objects.