Here, we discuss the ingredient list for What Goes into a Wood Stringer Pallet and Wood Block Pallet.
I want to take this opportunity to formally introduce an old friend of mine, the wood pallet. The pallet is a form of tertiary packaging. Let’s stop for a moment for some definitions:
Primary Packaging: Primary packaging is the first layer of packaging that directly encloses the product. It protects the product from damage, contamination, and spoilage while providing the consumer with essential information. Examples include bottles, cans, blister packs, and wrappers.
Secondary Packaging: Secondary packaging groups multiple primary packages together for easier handling, transportation, and storage. It often serves a marketing function by displaying branding and product information. Examples include cardboard boxes, cartons, and shrink wraps containing several items.
Tertiary Packaging: Tertiary packaging is used for bulk handling, storage, and distribution of products. It ensures that secondary packages are efficiently transported and protected during transit. Common examples include pallets, stretch wraps, and corrugated fiberboard boxes that consolidate secondary packages.
These three levels of packaging work together to ensure that products reach consumers in optimal condition from the manufacturer to the retail shelves.
As for the pallet, it is a flat structure used as a base for palletizing goods. The MH1-2016 standard defines the pallet as a “portable, horizontal, rigid, composite platform used as (a) base for assembling, storing, stacking, handling and transporting goods as a unit load; often equipped with (b) superstructure.” The superstructure is the assembly attached to the pallet’s supporting base.
Pallets are used to stack, store, protect, and transport materials when interacting with materials handling equipment such as forklifts, pallet jacks, conveyors or pallet racking systems. The pallet is the most common base for the unit load, which includes the pallet and goods stacked atop it, typically secured by stretch wrap, strapping, shrink wrap, adhesive, pallet collar, or other means of stabilization, including reusable wraps, straps, and nets. This definition applies to wood pallets and pallets manufactured from other materials such as plastic, composite, metal and paper.
Stringer and block pallets represent the two dominant construction styles in North America and Europe. For a high-level comparison and broader context, see our wood pallets overview.
What Goes into a Wood Stringer Pallet?
The ingredient list for a wood stringer pallet is the kind I’m looking for when I need to cook. It is a short one!
It includes the wood components and the fasteners that hold them together. The wood stringer pallet consists of the top deck (often deckboards but perhaps a panel), stringers and bottom deck boards. Steel fasteners hold these components together
Top Deck Boards
The top deck boards are the flat pieces of wood that form the top of the pallet. Typically, they are ⅜”, ½”, ⅝” or thicker, and 3 ½” or 5 ½” in width, but all of these dimensions can vary, depending upon the use case and material availability. Thicker material or more dense wood species can help improve pallet performance where needed.
Don’t forget about deck board placement. The corners of the boxes are the strongest part of the box structure and are designed to carry the weight of the box and its contents. Aligning these corners with the deck boards means that the boxes can effectively utilize their structural strength to support the weight of the unit load. Another important deck board design component is the butting of lead or end boards. Pallet lead boards must stand the test of being impacted by forklifts. Butting two nominal 6” lead boards (but really 5 ½”) can result in up to a 38% improvement in pallet durability, according to Virginia Tech.
Stringers
The stringers run perpendicular to the deckboards. In softwood pallets, they are often “nominal” 2x4s (1 ½ x 3 ½” actual measure), although usually thinner for hardwood. Another quick definition:
Nominal dimensions: The nominal dimensions refer to the initial size after milling before it is kiln-dried and dressed at the sawmill. The ‘actual’ dimensions refer to the final size that is used to build pallets.
Okay, let’s return to our discussion of stringers. These vertical members provide the main support structure for the pallet. Stringers can be likened to the spine of the pallet, distributing the load evenly across the structure and ensuring the pallet’s stability and strength. The standard pallet design usually includes three stringers, which can be adjusted based on the intended load capacity.
Adding more stringers effectively shortens the span between them, reducing top deck deflection under load. Likewise, by using a wing pallet – moving the stringers away from the edge of the load toward the center – you can also reduce the span and improve pallet strength without adding extra material. But wing pallets can present other issues. Once, I snagged the cuff of my jeans on the edge of a wing pallet and went flying. I could have used some wings myself!
Base or Bottom Deck
The bottom deck of a pallet provides additional stability and functionality. Bottom deck design is an important consideration for pallets that must be carried on conveyors or palletized loads that will be racked or stacked on top of other loads.
Stringer pallets typically have a unidirectional base, with all the deck boards oriented in the same direction. For example, the GMA-style pallet has five unidirectional bottom boards. When designing a pallet that must be conveyed, having the boards run perpendicular to the rollers will provide smooth conveyance as opposed to bottom boards parallel to the rollers. This orientation can result in a bumpy ride if rollers are too far apart. Where unit loads are to be stacked, having more bottom deck board coverage helps distribute weight more uniformly to prevent product damage.
Now, let’s talk about the fasteners, the unsung heroes that hold these components together.
Fasteners
Fasteners are critical to the structural integrity of the pallet. The choice of nail type, size, stiffness and application method can significantly influence the pallet’s strength and durability. They include driven nails and staples, bolts, wood screws, and lag screws. Most pallets utilize one of two types of nails, each known by alternate names. These include helically-threaded or drive-screw nails and annularly threaded or ring-shanked nails.
Helically threaded nails feature continuous spiral threads along the shank. Annularly threaded nails come with numerous rings along the shank that help grip the wood and prevent nail withdrawal. Of the pair, helically-threaded or drive-screw nails are the most popular choice for automated pallet assembly. Both types, however, are widely used by pallet manufacturers.
We’ll return to this point in a later chapter, but fastener stiffness and size are important, and the number of fasteners also matters. High stiffness ensures the nails hold the pallet boards firmly together, maintaining the structural integrity of the pallet during handling, storage, and transportation. Stiff nails contribute to the durability and longevity of the pallet, minimizing repairs and replacements.
Pallets designed for heavier loads may also use bolts or screws in addition to nails for added strength.
What Goes into a Wood Block Pallet?
The block pallet has become increasingly visible in North American supply chains in recent decades. While it only accounts for around 20% of U.S. new pallet production, its market share has doubled since 2011. The block pallet’s versatility, enabled by full four-way entry, makes it highly prized in industries such as grocery, plastics/chemicals, and others.
When I first began in grocery distribution over forty years ago, we used mainly stringer pallets. However, the loaders prized block pallets because they could be turned sideways to load, so they had a better chance of getting the last two unit loads (alright, I plead guilty after all these decades. We used to talk about getting the last two “skids” on the load, which was incorrect usage).
In those days, we did not have block pallets, but Kraft Foods used to send us products on yellow block pallets, and after they were empty, we would “borrow” them for loading. Not surprisingly, in hindsight, Kraft phased out sending them to us, and we were forced to start buying block pallets for ourselves.
Block pallets can provide substantial productivity gains in maneuvering unit loads on cramped loading dock conditions or expediting the quick unloading of trailers. But what goes into making a block pallet, and which version is best for you? In this installment, we look at the anatomy of the block pallet, including wood components and fasteners.
What Goes into a Block Pallet?
Top Deck and Stringerboards
Let’s start at the top and work down. Wood deck boards typically comprise the top deck, although solid plywood or wood composite sheet material is sometimes used. Solid decks are valued in applications such as bagged goods that could settle between the deck board gaps and become damaged or for small items that might not be adequately supported with typical deck board spacing. Adding handholes in a solid top deck can facilitate easier manual handling.
Immediately under the top deck boards are the stringer boards. As seen in the image, the stringer boards are sandwiched between the top deck boards and the tops of the blocks, providing additional support and helping to distribute weight evenly. In a reversible block pallet (a pallet that can be used with either side up), there would also be stringer pallets sandwiched between the bottom of the blocks and the bottom deck boards.
Blocks
Blocks are the defining namesake feature of block pallets and the key differentiator compared to stringer pallets. Positioned typically in a three-by-three grid, they anchor the top and bottom decks. Blocks can be cut from solid timber or formed from wood composite material. Some blocks are occasionally made by fastening multiple layers of solid wood boards or plywood together.
Composite blocks are popular for export pallets due to their uniform size and dryness, which aid in robotic placement and high-speed production during pallet manufacturing. However, they are not universally favored due to concerns about the possibility of fiber shedding. This risk is addressed using different bonding agents and higher pressure during block formation.
Bottom Deck
Bottom deck boards are attached to the block bottom for non-reversible pallets. Typical pallet bottom configurations include the parallel base, picture frame (perimeter) base, and the cruciform base. The bottom deck boards run in the same direction in a unidirectional or parallel base. Block pallets with a parallel base, such as europallets, can be nested together by flipping over every second pallet, interlocking them to increase transportation and storage efficiency.
Other bottom deck configurations include the perimeter base and the cruciform base. In perimeter base pallets, the bottom boards create a “picture frame” around the outside edge of the pallet, often with one or two center bottom components. The cruciform deck pallet is similar to the perimeter deck, with the addition of centerboards that are oriented in both directions. The advantages of these latter formats, particularly in the case of the cruciform base, are that they provide additional bottom deck coverage to distribute weight more evenly, and secondly, having bottom boards running in both directions enhances functionality with conveyors, regardless of the direction of travel.
Fasteners
Unlike stringer pallets, block pallets often use multiple nail sizes in the same pallet. For example, top deck board fasteners driven through the stringer board and into the blocks need to be longer, while nails fastening the top deck boards to the stringer boards (a combination referred to as the top mat) are shorter. Longer nails would drive through the deck board and the stringer board, leaving exposed nail tips that would be a hazard to material handlers.
In a heavy-duty block pallet, a typical configuration might be 3” annular ring nails for top deck boards being driven through the stringer board into the block, 1 ⅝” smooth shank nails for deck boards being affixed to the stringer boars (the mat), and 2 ¼” annular ring nails to fasten the bottom deck to the blocks.
Pallets Made of Other Materials
Pallets are also made from plastic and, to a lesser extent, from composites, metal and paper. The anatomy of these alternative material pallets is somewhat similar. We’ll dig into these options a little later, but here is an overview.
Plastic pallets typically have a top deck, blocks (or posts), and a bottom deck, except for nestable distribution pallets. Plastic stringer pallets exist in the marketplace, although they are less popular than block-style plastic pallets. Typically, plastic pallets are molded and do not rely on fasteners, although plastic components are sometimes welded together. Extruded plastic composite material is sometimes joined with screws. Steel or fiberglass inserts improve the stiffness and strength of plastic pallets. Adding rubber grommets or surface texture can help make the pallet deck less slippery.
Corrugated and steel pallets also have the basic features of a top deck or face and superstructure (beam or block). Some have a bottom face, and some do not.
Ultimately, when looking at what goes into a wood stringer pallet or a block pallet, the list of ingredients is fairly simple – but more complex for block pallets, making it more challenging to assemble.
Rick LeBlanc, EMBA, is the founder and editor of Reusable Packaging News (subscribe to the free newsletter) and editor of Western Pallet Magazine. A supply chain journalist with more than 30 years of experience, he specializes in pallets, reusable packaging, material handling and related operations. Rick is co-author of Pallets: A North American Perspective and Pallets & Progress: A Collected History of Pallets and Palletized Handling 1922–1945. He is also an advisory board member of the Virginia Tech Center for Packaging and Unit Load Design. Read Rick’s full bio.
