How heavy shelves are the main rack?
Two separate sets of shelves require four columns, but they can be turned into one column, requiring only three columns. The second shelf is attached to the first set of shelves, so it is called a rack (or subframe). The more quantity, the better for the customer.
An independent group has two columns and a few beams (plywood). If you assemble several groups into one column, you can share one column with the other one in front of it, except that the first group needs two columns. This can save space and reduce costs.
General shelf is composed of columns, beams and plywood assembled.
