Knot
A knot is the remains of a branch embedded in a board, visible as a round or oval area of cross grain. The Uniform Standard limits sound knots to one half of the cross-section on reusable pallets and seven eighths on single-use pallets, with tighter limits for unsound knots and holes.
Also called sound knot, unsound knot, knot hole
Reviewed
On this page
Knot limits in the Uniform Standard (2012, Table 1)
| Defect | Reusable | Single-use |
|---|---|---|
| Sound knots | up to 1/2 of the cross-section; at most 2 maximum-size knots per 6 in | up to 7/8; 1 per half length |
| Unsound knots and holes | up to 1/4 | up to 1/3 |
A sound knot is solid and tight in the board. An unsound knot is loose, decayed or has fallen out, leaving a hole.
Why knots matter
Grain bends around a knot, so a knot reduces bending strength, especially in the tension (bottom) face of a board or stringer. A large knot at a nail line also leaves less sound wood to hold the nail. For stringers, knots near the notch are the most critical, since the notch already reduces the section.
Grades and knots
The PDS component grades (Select, Premium, Standard, Utility, Economy) and their "&BTR" mixes are defined largely by limits on knots and other defects. The reusable column above roughly matches PDS Standard grade. See lumber grades.
Questions
- Do knots weaken pallets?
- Yes, they reduce bending strength, which is why the Uniform Standard limits their size and number by use class.
Related
- Pallet lumber gradesPallet lumber grades set limits on knots, wane, splits, decay and slope of grain. Reusable pallets need roughly PDS Standard grade; single-use roughly Economy.
- Slope of grainSlope of grain is how far wood fibers run off a board's long axis. The Uniform Standard allows at most 1 in 4 on both reusable and single-use pallets.
- WaneWane is bark or missing wood along the edge or corner of a board, left from the log's outer surface. The Uniform Standard limits it by part and use class.
- SplitA split is a lengthwise separation of wood fibers through a board. The Uniform Standard limits deckboard splits to one third of length on reusable pallets.
- Lead boardA lead board is the outermost deckboard at each end of a pallet deck. It is usually wider than interior boards, e.g. 5-1/2 in vs 3-1/2 in on a GMA 48x40.
- Load overhangLoad overhang is when product on a pallet extends past the pallet's edges. It leaves carton edges unsupported, cutting stacking strength and inviting damage.
Sources
- Uniform Standard for Wood Pallets (NWPCA, now Woodpack Global), 2012 edition