The difference between galvanized flat steel 40*4 and galvanized flat steel 80*8 is the difference on the material list!
There are many kinds of flat steel, Q235A/B/C, mainly depends on the location of your specific requirements, what is needed?;
Here, your galvanized flat steel refers to the basic matrix is carbon content less than 0.18% carbon steel (Q235), after galvanizing (general hot plating), play the role of surface oxidation resistance, corrosion resistance. Generally used in the power sector, what you mention is the difference in size.
