The external dimensions, internal dimensions, external void, internal void, or external and internal diameters of storage racks refer to their length. The external dimensions, external void, and external diameter of storage racks all mean the same, referring to the same size specification. The internal dimensions, internal void, and internal diameter of storage racks are synonymous, indicating the same specification. The difference between these two concepts is whether the length of the storage rack includes the specifications of the upright posts.

External dimensions, external space, and external diameter refer to the length measurements of storage racks that include the specifications of the uprights. Internal dimensions, internal space, and internal diameter refer to the length measurements of storage racks that do not include the upright specifications.

The distinction between outer and inner dimensions in the industry is due to certain items needing to be stored on warehouse racks in units of pallets, skids, or boxes. This is to prevent waste of storage space and ensure convenient access to goods, so these two specifications are used to indicate the dimensions of the warehouse racks.