Looking At the Effect of Pallet Fastener Quality on Pallet Durability

There are three common types of nails that are used in pallet construction: helically threaded, annularly threaded, and plain shank. Plain shank nails are regular nails with a smooth shank. Helically threaded nails have continuous spiral threads along the shank. Annularly threaded nails have a series of rings along the shank that grip the wood and help to prevent the nail’s withdrawal. The effectiveness of pallet nails is dependent on a variety of parameters including head diameter, wire diameter, thread crest diameter, thread angle, helix, flute, thread length, and effective nail length.

The Uniform Standard for Wood Pallets (NWPCA, 2014) lays out guidelines for nailing pallets. Nails used must penetrate the pallets’ block or stringer to at least a certain depth. For deckboards with thicknesses over 12.7mm., nails must penetrate at least 31.75mm., while for deckboards with thicknesses of 12.7mm. and under, nails must penetrate at least 1 in. The standard also defines the minimum number of nails that must be used per connection. For example, a minimum of two nails must be used for deckboards that are a width of 133.35mm. or less, and a  minimum of three nails must be used for deckboards that are 133.35mm in. to 177.8mm wide. Nails must also be arranged in a way that minimizes the splitting of the wood and must have a minimum head-to-shank ratio of 2 (except for new, reusable pallets, which need to have a ratio of 2.25). This standard also defines minimum nail quality based on the fastener withdrawal resistance (FWI) and the fastener shear resistance (FSI). The minimum FWI is 65 for multiple-use pallets and 50 for limited-use pallets, and the minimum FSI is 55 for multiple-use pallets and 40 for single-use pallets.

More details please refer to white paper done by Virginia Polytechnic Institute and State University