Strapping machinery crates and heavy skids: what strap should and should not do

A machine leaving a workshop on a skid, or inside a timber crate, combines several packaging jobs. Strap does some of them well and must not be asked to do the others. Getting that division right is the first decision in any machinery packing specification, and it shapes every choice about strap, closures and crate design that follows.

Three jobs, three solutions

Job	Usual method	Role of strap
Fixing the machine to the skid	Bolts, brackets, blocking and bracing designed for the machine’s mass and centre of gravity	Not the primary fixing
Closing and reinforcing the crate	Nails or screws, battens and strap around the crate	Holds panels and lid together, resists bursting, bundles loose parts
Securing the crate in the transport unit	Blocking, bracing and lashing to the container, trailer or flat rack	Lashing is a separate system with its own design and rating

The IMO/ILO/UNECE CTU Code, approved by the three organisations in 2014, is the non-mandatory reference for packing and securing cargo in containers and other cargo transport units. It treats securing as an engineered arrangement. A strap that closes a crate is not part of that arrangement unless it has been designed and rated for that purpose.

Choosing strap and closures for heavy crates

Steel strap and seals are a familiar choice for heavy timber crates and skids. ASTM D3953 covers flat steel strapping and seals for uses including closing, reinforcing, bundling, palletising and bracing. Woven polyester strap with wire buckles, and PET strap with clips or friction welds, are alternatives for many crates, particularly where operator handling and cut risk are concerns.

Four points usually drive the choice:

• Timber movement. Wet timber can shrink as it dries and loosen the straps. A November 2024 strapping guide from the distributor Spicers notes that steel’s lack of elasticity can be a problem on settling or shrinking loads such as lumber, while polyester keeps the load compressed after settling. A steel-strapped crate built from fresh timber may need re-tensioning, or a design that tolerates movement.
• Edges and protrusions. Battens, metal corner fittings and bolt heads can cut or kink strap. Plan edge protection at every point where the strap changes direction.
• Storage. Machinery crates often wait outdoors at a port or project site. Ask about the finish of steel strap and closures, and about UV exposure for plastic strap.
• Closure access. The seal or buckle must sit on a flat face where the tool can work and the joint can be inspected.

Skid and crate details that help strapping

• Provide strap slots or notches under skid runners, so the strap passes beneath without being crushed when the unit is set down.
• Position straps over cross members or internal battens, not over unsupported panel spans.
• Keep straps clear of fork entry points and lifting positions, and mark those positions clearly on the crate.
• Never lift a crate by its packaging strap unless the arrangement has been designed, rated and marked for lifting.
• Fit corner protectors where the strap crosses the lid edges and the runner ends.

A strap that sits across a gap between battens can deflect a panel inwards and lose tension. Moving the strap position on the drawing so that it sits over a batten costs little at the design stage and can save a re-strap at the port.

Timber rules and packaging law

Solid wood used to pack goods for international shipment, including dunnage, falls under ISPM 15, the international standard on wood packaging material, which requires approved treatment and marking. Wood processed so that it is free of pests, such as plywood, is excluded. Check which parts of each crate are solid wood and make sure those parts carry the required mark.

Within the EU, Regulation (EU) 2025/40 is due to apply generally from 12 August 2026. Its Article 29 re-use targets, which start on 1 January 2030, do not apply to packaging for large-scale machinery, equipment and commodities where the packaging is custom-designed for the ordering operator. That exclusion covers the re-use targets only; the regulation’s other packaging requirements still need checking for each crate design.

A handover checklist for the crate builder

Write down, for each crate type:

1. Machine mass, dimensions and centre of gravity, and how the machine is fixed to the skid.
2. Strap material, width, thickness and grade, with the closure type and tool.
3. Number and positions of straps, shown on the crate drawing.
4. Edge protection at each corner and protrusion.
5. The tensioning method and the check performed before dispatch.
6. Re-tensioning instructions for long storage, if needed.
7. ISPM 15 marking for solid wood components on export crates.
8. Who inspects the strapping at the port or site, and against which drawing.

Give the same document to the crate builder, the packing team and the freight forwarder, so that everyone is working to one revision.

Specify the closure with the strap

For steel-strapped crates, the steel strapping seal page sets out the widths and seal details to match with your strap and sealer. For woven systems, see woven strap and the heavier galvanized wire buckle variants. Send the crate drawing and strap details through the enquiry page; joint performance values are on request.