Helical nail
A helical nail (helically threaded or screw-shank nail) has spiral threads along its shank that make it rotate as it is driven, giving much higher withdrawal resistance than a smooth nail. It is the usual pallet nail for medium- and high-density hardwoods; a GMA-style 48x40 typically uses 2-1/4 in x 0.112 in helical nails.
Also called helically threaded nail, screw shank nail, SS nail, spiral nail
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How helical nails are specified
| Field | Example (PDS GMA-style sheet) |
|---|---|
| Fastener ID | 2-1/4 x 11-1/2 Ga. SS |
| Length | 2.25 in |
| Wire diameter | 0.112 in (11-1/2 gauge) |
| Thread length | 1.25 in |
| Thread crest diameter | 0.124 in |
| Flutes / helixes | 4 / 7.5 |
| Thread angle | 60 degrees |
| MIBANT | 36 degrees |
| FWC | 2.58 |
"SS" in a fastener ID stands for screw shank. Pitch equals thread length divided by the number of helixes.
When to use helical vs annular
Helical nails are generally recommended for medium- and high-density hardwoods and dominate automated nailing lines. Annular (ring-shank) nails are generally recommended for low-density hardwoods and most softwoods.
Why nail spec matters
Wire diameter and stiffness drive durability as much as the thread. Virginia Tech found a GMA pallet built with 0.112 in nails lasted about twice as many trips as one built with 0.099 in collated nails. The thread quality is captured by the fastener withdrawal characteristic. See pallet nails.
Questions
- What nails are used on a GMA pallet?
- Typically 2-1/4 in helically threaded nails with a 0.112 in (11-1/2 gauge) wire, 84 per pallet.
Related
- Annular nailAn annular (ring-shank) nail has rings around its shank that lock into the wood fibers. It is recommended for softwood and low-density hardwood pallets.
- Fastener withdrawal characteristicThe fastener withdrawal characteristic (FWC, Cw) rates how well a nail's threads resist pull-out. Plain nails score 1.0; reusable pallets need at least 1.9.
- Pallet nails: types, sizes and how manyPallet nails are usually 2 to 3 in helical or annular threaded nails, 11 to 12-1/2 gauge. A GMA 48 x 40 uses 84 nails: 2 or 3 per joint by board width.
- Pallet nail schedule: how many nails a pallet needsHow many nails a pallet needs: 2 per joint for boards up to 5-1/4 in wide, 3 up to 7 in, 4 up to 8 in (Uniform Standard). A 48x40 GMA pallet takes 84 nails.
- Kiln-dried lumberKiln-dried (KD) lumber is dried in a heated kiln to a target moisture content such as 19%. KD is not the same as ISPM 15 heat treatment unless marked KD-HT.
- KnotA knot is the base of a branch embedded in a board. The Uniform Standard limits sound knots to half the cross-section on reusable pallets and 7/8 on single-use.