Storage shelves are generally assembled by columns, beams, and shelves. An independent group has two pieces of columns. Such shelves are called main shelves.
If several groups of shelves are installed in a row, except for the first group that requires two pieces of columns, the other can share a column with the group in front of it. Except the first group is the main frame, the others are called Sub-frame. This can save space and reduce costs.
Since the shelves connected to the main and auxiliary racks must be moved along with the main rack, if it is a rack to be moved frequently, it is recommended to use all the main racks.