Pallet Racking Glossary

Welcome to our comprehensive Rack Safety Lexicon, your ultimate resource for all terms and abbreviations related to warehouse racking. At Damotech, we are committed to promoting a culture of safety in industrial environments, focusing on rack safety to safeguard your operations. Whether you're a seasoned industry expert or just starting your journey, our lexicon is your go-to reference, covering vital terms relating to warehousing, pallet rack storage and shelving. Explore our carefully curated glossary to strengthen your knowledge. What is a specific pallet rack component called? What is a pallet rack bay? Read our rack storage terminology guide and find out.

Pallet Racking System Parts / Components

Anchor bolts

A fastener used to secure a racking system to the concrete floor slab, so it maintains its position. The types of anchors most commonly seen in racking are wedge, screw, concrete strike and sleeve anchors. Typically made of steel, anchors vary in size and length depending on factors such as the weight and height of the rack, the levelness of the floor and seismic activity.

Base plate or footplate

A plate welded to the foot of a rack upright or repair unit to distribute the weight of the rack to the floor and allow it to be anchored. Base plate sizes vary from 3"x 5" to 5" x 7" in seismic zones and from 1/8" to 1/2" in thickness. Qualified engineers are required to assess the effective area and thickness of the base plate to ensure that the rack is supported and that the load is transferred to the concrete slab.

Bay / Rack bay

A rack bay refers to the space between two upright columns, in a racking system. A bay corresponds to the vertical superposition of cells. Rack bays can have a varying number of beam levels. Some companies use the number of bays in a warehouse as a means to estimate the price of the rack inspection and the engineering services.

Beam / Rack beam

A horizontal structural component of the rack system, usually arranged in pairs that bears the weight of the stored loads and transfers it to the uprights it is connected to. Common beam shapes are box beam, step beam and c-shape beams. Variations of these shapes exist. Ultimately, the beam's capacity depends on factors such as the beam shape, size, and material.

Beam connector (beam clip, beam bracket, end plate)

The rack component that facilitates the safe fastening of the support beam to the upright frame. The beam connector is a formed, stamped or punched metal part that may be clipped or bolted to the upright

Cell / Rack cell

A rack cell is a space on one beam level, between two uprights, which generally accommodates two pallet positions along its width. The size of the cell varies depending on the type of racking system.

Cross aisle tie

A horizontal component used to connect the top of two opposing rack frames to provide stability in the cross-aisle direction.  It can span across the warehouse aisle. Cross-aisle ties are specified by the designer of the rack system in the Load Application and Rack Configuration Drawings (LARCs).

Brace / Rack brace

Diagonal or horizontal members bolted or welded between frame columns in a specific pattern to form an upright. It is designed to resist cross-aisle forces imposed on the rack's frames and to improve the stability of the racking system.

Brace repair vs. upright replacement

Column / Upright column

The vertical component of a racking system, on which horizontal and diagonal braces are welded, and beams are attached. An upright column may bend or twist as a result of an accidental impact with material handling equipment, or buckle from excessive loading.

Column guard

A prevention device designed to protect against impacts to the rack column. Generally installed at its base, the column guard or post guard can be fixed to the floor slab in front of the rack column. It may also be tied or bolted directly onto the upright column. It is made of materials such as structural steel, shock-absorbing rubber or polyethylene (plastic).

Diagonal brace

A component that is either welded or bolted to the columns diagonally. They add resistance and rigidity to the upright frame, as they resist cross-aisle forces.

Double column

The front or rear frame columns are sometimes doubled to a certain height and usually welded together to create a built-up column section. Doubled columns can be used as reinforcement or for additional load capacity.

Floor system / Floor slab

The majority of racks are installed on a concrete slab. Like racking systems, a floor also has a maximum load capacity. The concrete slab must resist and transfer static and dynamic loads from the surface to the subsoil. The bearing capacity of a floor is found in the builder's original building specs or the contractor's plans for construction. If you cannot obtain this information, you can ask an engineer to determine your floor's capacity.

Horizontal brace

A component that is either welded or bolted to the columns horizontally. They add resistance and rigidity to the upright frame, as they resist cross-aisle forces.

Labels / Capacity labels

A method used to display the load capacity of the racking system. The information on the labels comes from the Load Application and Rack Configuration Drawings, aka LARCs. Load capacity labels are typically installed on the first beam level of each bay, at eye level. If beam levels have varying capacities, multiple labels can be printed and installed to inform the forklift operators.

Load capacity plaque

A plaque is a type of signage used to communicate the rated load capacity of a pallet rack system and the maximum weight it can hold. It should include the maximum beam capacity, the maximum bay capacity and the rack manufacturer's information. Moreover, a reference to drawing(s) or other approved documents that establish the maximum permissible load for a given rack bay can be included on the plaque. It should be placed where operators can read it. If all the information contained in the load plaque is standard for a bay, the aisle or a section of the rack, one plaque is sufficient for that area.


A flat structure used as a base for the storage and unitization of goods in the supply chain. Pallets are made of materials such as wood or plastic. They come in different sizes and configurations (two-way and four-way entry) based on the country and the industry they are used in.

Pallet stopper

A rack accessory used to stop a pallet from going too far into the rack and damaging it. A beam stop is fixed on the back of the system, and an angle stop is also set on the end with screws. Both devices prevent the fall of pallets, which may occur while placing or pushing a pallet into a bay. Pallet stoppers will also prevent excessive pallet overhang.

Pallet support bars

Steel components installed perpendicular to the load-supporting beams. They are intended to support a loaded pallet's weight in cases where the pallet cannot be placed directly onto a pair of beams.

Palletized unit load

A palletized unit load is defined as one or more items secured to a pallet or skid so that it may be handled and stored as a single unit.

Row spacer

A component used for the spacing of back-to-back pallet racks that provides added stability to the racking system and maintains an even spacing between the racks. The vertical distance between row spacers should be between 8' to 12' or 2.4 m to 3.6 m. They should be located at elevations that provide a direct load path between the columns of back-to-back frames.

Safety bar

A component installed perpendicular to the load support beam to prevent a load from falling through the rack. The bars may be attached to the beams or dropped over them. Safety bars are a recommended fall protection accessory, but they are not mandatory.

Safety pin

A small device or mechanical fastener (shear pin, screw bolt, etc.) installed on the beam connector will help prevent its accidental dislodgement from the upright frame column. In warehouse areas accessible to the public, it is advisable to use bolts. The type of safety pin, including size, material, and installation requirements, must be approved by the manufacturer or a qualified engineer.


Inserted between the concrete floor and the base plate of a rack, they must always match the size of the base plate. The material must have equal or greater bearing strength than the floor slab. To maintain the levelness of the racking system, stacking multiple shims is allowed. However, in no case shall the total thickness of a shim stack exceed six times the diameter of the largest anchor bolt used in the base plate. Moreover, shim stacks having a total thickness greater than two times the anchor bolt diameter under bases with only one anchor bolt shall be interlocked or welded together to allow for load transfer.


The word strut or rack strut is sometimes used to refer to the rack's diagonal and horizontal bracing components.

System / Pallet rack system

A pallet racking system refers to a carefully engineered and structured group of racking components organized as an autonomous entity to store and organize palletized goods within a warehouse or storage facility. This system typically consists of upright frames, horizontal beams, and various optional accessories, such as wire decking, support bars, and safety features, all configured to create efficient and accessible storage for pallets. The rack system design will determine the types, sizes, and weight of pallets that can be stored.

Upright frame / End frame / Rack frame

These terms refer to 2 upright rack columns (front and rear) and the bracing members that connect them. Their depth can vary.

Upright column

The upright column is the vertical part of the racking system or frame. Upright columns are commonly roll-formed and made of steel, in a "C" shape. Holes or slots are punched into the upright during the manufacturing process to allow for load support beams to be fixed or mounted to the upright columns.

Wire mesh decking

An accessory installed on pallet rack shelves to prevent stored merchandise from falling through the rack. Wire decking is made from welded-wire mesh and generally has reinforcing channels or support wires. Sizes of wire mesh decking vary depending on the manufacturer. Common sizing is 24", 36", 42" or 48" deep by 46", 52" or 58" long.

Pallet Racking System Types

Cantilevered rack

A racking structure furnished with cantilever arms that horizontally support long or cumbersome objects like pipes, lumber, carpet rolls, etc. The horizontal arms are fixed to the vertical columns with welds, bolts or brackets. This type of rack is not intended for palletized loads; however, it provides useful but low-density storage. Stored items are relatively easy to access in a cantilevered rack. They are susceptible to damage from forklifts considering damage can occur on the arms that jut away from the structure.

Double deep rack

This type of rack configurations allows for the storage of goods, usually palletized, two rows deep. Storage is density is thus increased. This rack system is ideal for high throughput operations. Most damages associated with double deep rack systems are caused by material handling equipment accessing the deeper pallet where the operator's view is obstructed.

Drive-in rack

Drive-in racking systems offer high-density storage by allowing a lift truck to travel deep into the rack for placement and retrieval of loads. Load- supporting beams at the base of the racking structure run the depth of the system. Loading and unloading within a bay are done from the same service aisle and consists of a last-in-first-out (LIFO) system. Forklift operators must be skilled in loading and unloading as the risk of impact is greater.

Drive-thru rack

This racking system is also a high-density storage option, as it allows forklifts to drive through the rack. Moreover, pallet loads are accessible from both ends or aisles of the racking system. Load rotation consists of a first-in-first-out (FIFO) method. They can be more expensive than drive-in systems, but provide more flexibility in the pallets' rotation order. Forklift operators must be skilled in loading and unloading operations as the equipment moves through the rack.

Dynamic rack

Dynamic racking systems are inclined and involve rollers that allow palettized loads to slide through the system. They include gravity pallet racks and mobile pallet racks, also called pallet flow or flow-thru, carton flow, and push-back systems.

Fixed rack

A fixed rack is one where the palletized load is loaded from the front. This category of storage racking includes single-deep, double-deep and stack systems.

Gravity rack

This type of racking system is dynamic. Pallet flow racks and push-back racks are gravity flow systems that rely on gravity to move palletized loads within the rack structure, on inclined rails. They maximize storage space but require regular maintenance.

Mobile rack

Mobile racking systems are configured much like static racks, but they can be moved. Compact, space-saving, and often motorized, these racks are set-up on rail systems that allow the movement of entire rows. The racking remains compact until it needs to be accessed. A service aisle is then created between two rows. Mobile systems are advantageous for maximizing storage space utilization, but their initial installation can be costly.

Pallet rack

Pallet racks, commonly referred to as pallet racking systems, are a specialized type of industrial storage solution designed to efficiently store and manage large quantities of goods, products, and materials on pallets within warehouses, distribution centers, and manufacturing facilities. These racking systems are engineered to optimize space utilization while facilitating the organized storage and retrieval of palletized items. One of the key advantages of pallet racks is their adaptability. The modular design of these systems permits easy adjustment of beam heights and configurations, accommodating items of varying sizes and quantities. Forklifts or other compatible lifting equipment are commonly used to load and retrieve pallets, allowing for efficient movement of goods within the rack system.

Pallet flow rack

This type of racking system is dynamic and uses gravity. Much like a conveyor system, pallet-flow lanes are installed on a slight angle to allow the storage of multiple pallets per level. Moreover, brakes are used to control the speed of the pallets. In such systems, loading and unloading is done on opposite sides of the rack structure, from two different service aisles.

Push back rack

This type of racking system is dynamic and uses gravity. Horizontal lanes are installed on a slight angle permitting deep pallet storage (up to 6 pallets). Loading and unloading is done at one end, from the same service aisle. As pallets are loaded, they push the other pallets backwards on the same row.

Single deep rack

A fixed vertical storage rack configuration that allows easy access to stored pallets, only one pallet deep. Single deep systems require aisles, thus using more floor space. This conventional system is low cost and accessible.

Shelf rack

Shelf racking, also known as shelving or storage shelving, is a versatile and efficient storage solution designed to organize and support the storage of various items in a wide range of settings, including warehouses, retail spaces, offices, and homes. This storage system typically consists of a series of horizontal shelves or platforms that are evenly spaced and stacked vertically, creating multiple tiers or levels for storing goods, products, or objects. Shelf racking is often used to store items that are not suitable for pallets, such as smaller products, tools, office supplies, electronic components, and more. There are various types of shelf racking, each designed to cater to specific storage needs. Common variations include boltless shelving, rivet shelving, wire shelving, mobile shelving, and more.

Static rack

Static racking is a broad category of racking. It includes fixed storage racks such as single-deep, double-deep and stack systems, as well as drive-in/drive-thru pallet rack systems.

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Pallet Racking Engineering Terminology

Column buckling

Column buckling occurs when a rack column collapses due to a large deflection perpendicular to the component's axis. This rack failure occurs suddenly when the stress exceeds the compressive yield strength of the material. Columns under concentric loading (load applied along the central axis) can be analyzed by using the Euler formula and Johnson Formula for long and intermediate columns. As for columns under eccentric loading (load offset from the central axis), maximum deflection and maximum compressive stress formulas are used.

Nominal strength / Nominal capacity

Nominal strength is the capacity of a rack structure or component to resist the effects of loads.

Out-of-plumb rack

Out-of-plumb refers to the verticality and maximum deviation from the plumb of an upright when adequately loaded. The out-of-plumb rack is straight but leaning, in either direction; down aisle or cross-aisle.  ANSI/RMI specification states the maximum ratio is 0.5 inches per 10 feet of height or simply 1/240 for an unloaded column.

Out-of-straight rack

An out-of-straight rack upright is one that has an "s" or bow shape. Any two points on the out-of-straight upright column should not exceed a ratio of 0.5 inches per 10 feet of height when loaded or simply 1/240 for an unloaded column.

Torsional buckling

When a rack component is subjected to loads that result in both lateral displacement and twisting, it is said to undergo torsional buckling.

Unit load

Fundamental to the efficient movement of products through the supply chain, a unit load is "handled" and can combine multiple items (boxes, products, containers) into a single unit. A warehouse or distribution center may handle different types of unit loads.

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Warehouse Rack Industry Vocabulary

Aisle / Rack aisle

The space between racking systems that allows forklift and personnel to maneuver in and around the racking systems. Their width is determined during the design phase. Standard aisle widths are recommended by equipment and lift truck manufacturers. If aisle space is inadequate for the handling equipment used, damage can occur.

Back to back racking

A standard rack configuration where the racking system is composed of two consecutive back-facing rows. Row spacers join the two parallel rows of upright frames.

Beam deflection

Beam deflection refers to the curvature of a supporting beam when loaded. It should not exceed L/180, L being the beam's length or span. For a typical 8' beam, the maximum deflection is approximately 0.5 inches. A beam deflection should not be confused with deformation, which is caused by overloading or damage resulting from an impact.

Building column

A building column is a vertical structural element that carries and transfers loads from a ceiling, roof, or beam to a floor slab or foundation. Not to be confused with a rack column, their shape and size will vary based on the building's design and layout. In a warehouse, they are vulnerable to damage by forklifts and can be protected using protection devices.


Clearance is the necessary space between the various elements surrounding racking systems; loads, walls, aisles, building columns and walkways. For instance, pallet racks should not be installed against a structural component such as a wall or building column. Different types of systems require different clearances. Rack manufacturers and RMI's Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks can provide guidance.

Counterbalance lift truck

A counterbalanced lift truck is a common piece of powered equipment used in the warehousing and material handling industry. It loads and unloads materials and pallets, generally indoors. Weight at the back counterbalances the carried load, hence its name. Operators stand or sit in this forklift considered a class 1 industrial truck.

Flue space

A flue space is a clearance within a racking system that allows fire and heat to vent vertically and horizontally. The longitudinal and transverse flue spaces refer to the spaces between the rows of storage perpendicular and parallel to the loading direction, respectively. Inadequate or blocked flue spaces can prevent sprinklers from working effectively. Row spacers can be installed to provide precise longitudinal flue space within a rack system.


A forklift, or forklift truck, is a powered vehicle equipped with prongs or forks in the front for lifting and moving palettized loads. This indispensable piece of warehousing equipment comes in various forms: counterbalanced lift trucks, narrow-aisle straddle trucks, reach forklift trucks, side loader trucks or order picking trucks. They can be operated while seated or standing.

Load capacity

It is the maximum load permitted to be handled or placed on the rack under specific conditions. Several elements, such as the height, type, and configuration of the rack, will determine its capacity to bear loads.

Order picking truck

This powered lift truck is designed to restock or fill orders manually when piece-part or case picking is needed. The operator can be raised several meters to load or prepare orders of quantities smaller than a single pallet. An order picking truck can circulate in narrow aisles and reach heights of up to 30 ft. The platform on which the worker stands must be protected with a guardrail. He must wear a safety harness to ensure his safety.


Outriggers are the part of the forklift truck that extends outwards at the base and contributes to its stability. They are also called base leg openings. Forklifts have two legs with one or two wheels that project forward and distribute the load to stabilize it. They are often responsible for damage found at the very base of the racking systems.

Pallet jack

The pallet jack is used for lifting and moving palletized loads over a short distance. More compact and less costly than forklifts, this versatile piece of equipment can be manual or motorized (electric). The pallet jack is steered by a 'tiller' like a lever that also acts as the pump handle for raising the pallets.

Reach truck

A forklift with an extending scissor mechanism that allows a further reach into double-deep racking.

Roll-formed pallet rack

This standard type of rack is made of thin steel and is cold-formed with holes punched through. This option is economical and derives its strength from its shape.

Row / Rack row

A row comprises of a series of rack bays arranged side by side to form a section of a racking system.

Seismic zone

A region that is prone to earthquakes and seismic activity, it requires particular rack design considerations. For example, in seismic zones, it is required to install 2 anchors per base plate to bolt down the racks to the ground.

Structural pallet rack

A type of rack made of structural steel that has a strong weight-bearing capacity with beams bolted onto the upright frames. It is typically used for higher density applications like pushback, drive-in, and pallet flow applications but can be used for selective racks as well. They are a heavier gauge and "C" shaped.

Tunnel bay

A cross-aisle passageway that goes right through a warehouse racking system. It allows the passage of equipment or personnel through the system. To be done safely, it must be approved by the rack manufacturer or a qualified engineer.

VNA (Very Narrow Aisle)

This term refers to a very narrow aisle space used to maximize storage by reducing the distance between racks. Due to the restricted width of VNAs, standard forklifts cannot be used to load and unload pallets. Narrow aisles require lift trucks intended for this application, such as narrow aisle straddle trucks, swing reach trucks, order picking trucks or turret trucks.


A path or space reserved for pedestrian traffic in a warehouse. Some facilities choose to place paint, markings or signage to establish walkways while others choose to put guardrails or fences to separate people and equipment in the aisles.

Wall spacer / Wall tie / Wall bracket

A device used to connect an upright frame to an adjacent wall. It ensures a consistent space and clearance between the racking system and the wall of the building. The use of a wall spacer is not recommended since rack systems are meant to be a free-standing structures.


A warehouse is a specialized facility or commercial structure primarily intended for the systematic and efficient storage, handling, and management of a wide range of goods, products, or materials. These facilities are crucial components within supply chain and logistics systems, serving as pivotal points where raw materials, finished products, or inventory are temporarily stored, organized, and sometimes processed before distribution, sale, or further manufacturing. Warehouses are equipped with various infrastructure and technology, such as shelving, pallet racking, forklifts, and inventory tracking systems, all designed to optimize storage space, facilitate easy access, and ensure the safekeeping of items. These versatile spaces play a pivotal role in the smooth flow of goods from manufacturers to consumers, helping businesses maintain inventory control, meet customer demands, and streamline their overall operations.

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Warehousing and Material Industry Associations & Abbreviations

ANSI (American National Standards Institute)

ANSI - American National Standards Institute - Logo

American National Standards Institute is a private, non-profit organization founded in 1918. Its mission is to improve the global competitiveness of U.S. businesses and the quality of life of Americans by encouraging and facilitating voluntary consensus standards and conformity assessment systems and upholding their integrity. More than 270,000 companies and organizations and 30 million professionals worldwide are represented and served by ANSI.

CSA (Canadian Standards Association)

CSA - Canadian Standards Association - Logo

The Canadian Standards Association was founded in 1919. It is a leader in standards development, testing, inspection, and certification worldwide, including in Canada, the U.S., Europe and Asia. A new CSA guideline on steel storage racks, CSA A344-17, was published in 2017.

LARC (Load Application and Rack Configuration)

Load Application and Rack Configuration or LARC drawings are documents required for the safe use of storage rack systems. These drawings are provided by the rack manufacturer when the racking system is first installed. They can also be evaluated and amended by a qualified engineer. They contain the load capacity of the rack and their configuration. The information displayed on the load plates and labels comes from these configuration drawings. Read more


MHI - Material Handling Institute - Logo

MHI is America's largest material handling, logistics and supply chain association. Members are mainly manufacturing companies and supply chain professionals. The association has strong industry groups who engage in knowledge sharing to drive innovation and establish standards. MHI also organizes annual trade events such as MODEX and PROMAT to showcase its member companies' products and services and to educate the industry on new solutions.


OEM stands for Original Equipment Manufacturer, a company that sells its goods to distributors or end-users. For example, a rack manufacturer is the original equipment manufacturer that can be contacted when a rack component needs replacement.


OSHA - Occupational Safety and Health Administration - Logo

Occupational Safety and Health Administration or OSHA is an agency of the United States Department of Labor created by Congress under the Occupational Safety and Health Act of 1970. It was created to ensure safe working conditions for all American workers. OSHA has established and enforces safe workplace practices by offering education, training, inspections, and assistance.

PROGMA (Protective Guarding Manufacturers Association)

ProGMA - Protective Guarding Manufacturers Association - Logo

The Protective Guarding Manufacturers Association, of which Damotech is a member, gathers the industry's leading suppliers of fixed protective guarding products. Together, they offer educational materials to advance proper protective guarding methods and promote safety and security in all warehouses.

PSR (Pre-start Health and Safety Review)

A PRS or PHSR is a review process required in Ontario, Canada to certify that storage racks are safe to use.  The inspection process and report are done by a knowledgeable person to determine if the rack systems are compliant. It must contain recommendations on what to do if they are not.  Read more


It's a voluntary program for manufacturers of industrial steel storage racks. This certification ensures accordance with RMI's ANSI MH16.1-2012 Guidelines. It signals that the manufacturer has the technical and manufacturing skills to produce safe racks that meet the RMI's codes and standards. Rigorous analysis, testing, and calculations are done before the manufacturers can display the R-Mark license on their products.

RMI (Rack Manufacturers Institute)

RMI - Rack Manufacturers Institute - Logo

The Rack Manufacturers Institute gathers the industry's leading suppliers of industrial steel storage racks and related structural systems. Its members supply industrial rack solutions worldwide in virtually every major manufacturing and distribution sector. Formed in 1958, it continues to develop and advance national standards for industrial steel storage racks and related products. It funds product testing and R&D programs for technological advances and education. Damotech is a proud associate member of RMI.

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