A stacking frame, also known as a portable stacking rack or pallet frame, is a specialized piece of material handling equipment designed to be placed on a pallet or act as a standalone unit. It consists of a base and removable posts or a fixed superstructure. These units are engineered to interlock or nest securely when stacked, creating a stable, multi-level storage structure. This design transfers the weight of the upper loads through the frame's posts directly to the frame below, bypassing and protecting the goods on the lower pallets from being crushed.

A. bin: A bin is a container for holding items, especially loose materials. While some bins are stackable, they do not function as a frame to protect a separate load.

B. pallet rack: A pallet rack is a large, stationary storage structure with horizontal beams for storing palletized loads. It is a fixed installation, not a portable unit that interlocks with the load itself.

D. storage rack: This is a general term encompassing many types of storage systems, including pallet racks. It is not specific enough to describe the portable, interlocking device in the question.

1. Bartholdi, J. J., & Hackman, S. T. (2019). Warehouse & Distribution Science. Georgia Institute of Technology. In Chapter 5, "Storage and handling equipment," portable stacking racks are described as a flexible storage medium: "These are steel frames on which pallets may be set. The frames are designed to be stacked on top of one another. This is useful for temporary storage... and for items that cannot be stacked on top of each other." (Section 5.1, Storage Media).

2. Material Handling Industry (MHI). (2022). MHI Terminology. MHI defines a "Stacking Frame" as: "A tubular steel frame which is placed on a pallet to permit stacking of pallet loads of fragile or odd-shaped items without danger of crushing the products on the bottom pallet."

3. Kulwiec, R. A. (Ed.). (1985). Materials Handling Handbook (2nd ed.). John Wiley & Sons. Chapter 11, "Pallets, Containers, and Packaging," describes pallet stacking frames as accessories that "permit stacking of crushable or irregular-shaped loads... The frames carry the load of the pallets stacked above." (p. 489).