Putting a nail or screw into a wooden pallet sounds simple enough, but it can actually get quite technical. When there is a failure, a good set of photos is often enough for an engineer to identify if the problem is the fastener or something else entirely.
There are many measurements that determine the withdrawal strength of a nail. The snapshot above details four different types of fasteners. In general, helical (screw) nails are better suited for harder wood species, and annular (ring) nails hold better in softer species.
Here are some more notes:
- Most common nail spec
Most pallet specs do not include enough information to guarantee a good fastener. The most common nail spec we see is 2-1/4” Helical nail. This can be everything from a very good nail with very high withdrawal strength to a very small diameter nail that is little more than a big tack.
- Cheap nails
Moving from a cheap nail to a good nail only adds about 2% to the pallet price, but will double the life of a pallet. The cost vs performance tradeoff of a good nail is often a great deal. This is true even with one-way pallets because you’ll see fewer failures and better handling in the field. But, if a pallet user does not require the better nail, they will likely get the cheaper ones.
Common Fastener Failures
Following are a few insights on fastener problems and solutions for wood stringer style pallets:
- Broken deckboards
If deckboards are broken, the fastener likely did its job and the boards were too weak for the application. You need a stronger deckboard (thicker, wider, hardwood, etc.).
- Boards pulling from stringers
If you have good boards pulling from the stringers (and you see nail points sticking from the boards) then the fastener pulled out of the stringer. The nails did not have enough withdrawal resistance for the application.
The best way to spec a nail is to give some guidelines, such as “2-1/4” helical’, and then also reference the Uniform Standard for Wood Pallets. This standard specifies minimum performance requirements for withdrawal in nails. Unfortunately, many pallet manufactures do not use this standard and may continue to use a sub-performance nail.
Are fasteners the issue in your pallet failures? Send me photos. I can offer an evaluation to see if fastener withdrawal is contributing to the issue.