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Glossary

Fastener withdrawal characteristic

Also called: FWC, Cw, withdrawal characteristic

Reviewed

Definition

The fastener withdrawal characteristic (FWC, written Cw in the Uniform Standard) is a multiplier that rates how much a nail's threads improve its resistance to pulling out. A plain-shank nail scores 1.0; the Uniform Standard sets minimums of 1.9 for reusable pallets and 1.5 for single-use pallets.

On this page
  1. How FWC is calculated
  2. Typical values
  3. Minimums in the Uniform Standard (Table 4)
  4. Why it matters

How FWC is calculated

The Uniform Standard (2012, Annex F) gives a public formula based on the nail's geometry:

Cw = 1 + K x (thread crest diameter - wire diameter) x (H / thread length)

K is 22 for helical nails and 60 for annular nails, and H depends on the thread count and angle. For the 2-1/4 in x 0.112 in helical nail on the PDS GMA example (0.124 in thread diameter), the result is 2.58, matching the spec sheet.

Typical values

Nail FWC
Plain shank 1.00
Helical and annular pallet nails (PDS sheets) 2.58 to 3.69

Minimums in the Uniform Standard (Table 4)

Reusable Single-use
Minimum Cw 1.9 1.5
Minimum head-to-shank ratio 2.25 2.00

Why it matters

Withdrawal strength decides whether deckboards stay tight after repeated handling. FWC multiplies the basic withdrawal equation, so a nail with FWC 2.58 resists pull-out about 2.6 times better than a plain nail of the same wire size in the same wood. See pallet nails and MIBANT.

Questions

What is a good FWC for pallet nails?
At least 1.9 for reusable pallets under the Uniform Standard. Quality threaded pallet nails on real spec sheets run about 2.6 to 3.7.

Sources