Pallet racking
Pallet racking is a material handling storage aid system designed to store materials on pallets (or "skids"). Although there are many varieties of pallet racking, all types allow for the storage of palletized materials in horizontal rows with multiple levels. All types of pallet racking create some level of increase storage density with the least dense being the least expensive and cost increasing with storage density. Forklift trucks are usually an integral part of any pallet rack system as they are usually required to place the loaded pallets onto the racks for storage. Pallet racks are an essential and ubiquitous element in most modern warehouses, manufacturing facilities, retail centers, and other storage and distribution facilities.
Selective pallet racking is the most common pallet racking system in use today. Selective pallet racking typically come in one of two configurations: a
roll formed, or clip-in configuration, and a
structural bolt-together configuration.

Roll formed selective rack is most commonly manufactured in a "teardrop" style. The nickname "teardrop" comes from the fact that the holes on the column of the upright are shaped like a teardrop. Pallets then rest on the horizontal load beams that are held in place by mounting clips. Because the clips on teardrop configurations can be quickly moved, the shelves can be easily adjusted to different heights to accommodate various load sizes. This is convenient for a warehouse that needs to store a wide variety of product sizes.

Structural pallet rack systems are very similar to roll formed pallet rack systems except the horizontal load beams are attached to the uprights with bolts and have much greater weight-bearing capacity. Also, structural pallet racking can be designed into the structure of the building itself, so that the upright columns are simultaneously used to support the roof of the storage facility, in which case the structural pallet rack uprights replace the storage building's vertical support I-beams. This system is a rack supported building.
Very Narrow Aisle (VNA) is the use of selective pallet racking in a tighter configuration to provide maximum space utilization within a storage facility. These systems typically operate in conjunction with wire-guided or rail-guided reach-truck systems. A wire-guided system consists of a wire embedded in the concrete floor that provides tracking for the reach-truck. A rail-guided system consists of angle iron bolted to the floor down the length of each row.