The strength grade of nails used in pallet construction, from low-grade common nails to high-grade hardened pallet nails.
Detailed Definition
Nail stress grade is a trade term for how stiff and strong a pallet nail is. Pallet nails range from soft, low-carbon wire nails to stiffer nails made from harder wire or heat-treated after forming. Stiffness is usually measured by a bend test such as the MIBANT (Morgan Impact Bend Angle Nail Tester) test, in which a lower bend angle means a stiffer nail. Along with wire diameter, length and shank type, such as helical or annular threaded, nail stiffness strongly affects how well joints resist loosening, withdrawal and shear in use. ASTM F1667 covers driven fasteners such as nails.
Why nails decide pallet life
Most pallet failures in use start at the joints rather than in the wood. Every time a pallet is lifted, dropped, or pushed by forks, the nails are bent and pried. Soft nails bend and allow boards to loosen, which leads to broken deck boards and protruding nails. Stiffer threaded nails resist this better, which is why many durable pallet specifications call for hardened or high-stiffness nails, especially on top deck boards and in repaired pallets.
What to put in a nail specification
- Shank type: smooth, helically threaded or annularly threaded.
- Length and wire diameter, matched to board thickness.
- Stiffness, often stated as a maximum MIBANT angle.
- Head size and number of nails per joint.
- Clinching rules if nails go through and are bent over.
The NWPCA Pallet Design System includes fastener properties because nail choice changes both strength and expected durability. If a supplier substitutes a different nail, ask whether the design still meets the load and handling requirements. Also check nail heads are flush, since protruding nails damage product and are a common rejection reason.
Related Glossary Terms
Frequently Asked Questions
What is the MIBANT test for pallet nails?
MIBANT stands for Morgan Impact Bend Angle Nail Tester. A nail is clamped and struck by a weight dropped from a set height, and the angle the nail bends to is measured. A smaller angle means the nail is stiffer and more resistant to bending. Pallet specifications sometimes set a maximum MIBANT angle so that nails stay tight under handling, and nail suppliers can report values for their products.
Are threaded nails always better than smooth nails for pallets?
Threaded nails, either helical or annular, generally hold better than smooth nails of the same size because the threads resist withdrawal as wood dries and boards are pried. Smooth nails can work in some applications, especially with clinching, but they are more likely to loosen. The best choice depends on wood species, moisture, board thickness and how the pallet is handled, so treat nail type as part of the pallet design.