What Should Buyers Know About Coil Nails For Fence Manufacturing And Exterior Timber Assembly?

Prepared by: The Fastener Engineering Technical Committee
First published: November 2024
Revision 1.1: March 2025
Technical review: Licensed structural engineer (P.E.) and former AWC code development participant

Key takeaway: Most premature fence failures are not caused by bad lumber or poor workmanship. They trace back to a fastener that was the wrong size, wrong shank, or wrong coating for the environment in which it was installed. Coil nails solve a production problemfast, high-capacity drivingand a performance problemholding power in outdoor timberbut only when the entire specification stack is chosen deliberately.

Introduction

Procurement teams often treat coil nails as a commodity. The result is a purchase order that names only a length and the word galvanized. That is not a specification. It is a blank check written to a supplier, and the fence will pay for it years before its expected service life ends.

This bulletin walks through the six properties that actually govern performance, how they interact with board dimensions, environment, and tooling, and what to confirm before issuing a purchase order. It is written for fence manufacturers, general contractors, and distributors who buy coil nails in production volumes and want fasteners to be a controlled input rather than an unknown.

The Specification Stack: Six Properties That Determine Performance

A coil nail is defined by more than its length. Buyers should treat the following six properties as a single package, because changing one usually forces a change in another.

The governing dimensional and material specification for coil nails is ASTM F1667 Standard Specification for Driven Fasteners: Nails, Spikes, and Staples. Coatings are covered by separate ASTM standards, described in Section 5.

A purchase order that names only galvanized without a coating standard and class is not a complete specification. Suppliers will fill that gap with whatever is cheapest to run and the fence will pay for it years before its expected service life ends.

How these properties show up in the field

Length and Diameter: Matching the Nail to the Board

The most common shop rule is that nail length should be roughly three times the thickness of the piece being attached; the remaining shank length embeds in the receiving member. For example, a 1-inch picket fastened to a rail typically takes a 3-inch nail.

That is a starting point, not a design value. Structural design standards such as the National Design Specification (NDS) for Wood Construction reduce the allowable lateral load when penetration into the main member is limited. Assemblies carrying wind or impact loads should be engineered rather than estimated from the three-times rule. When in doubt, use the NDS withdrawal tables and lateral load equations, and carry a larger penetration rather than a longer cosmetic nail.

Diameter deserves equal attention. A larger wire diameter increases holding power but also increases splitting risk, particularly within roughly one inch of a board end. Consider two common fencing scenarios: a 16 pine picket on a 24 rail, and a 5/16-inch cedar picket on a 23 rail.

• For the pine picket, a 3-inch nail at 11 or 12 gauge with a ring shank and a diamond point will typically drive cleanly.
• For the thin cedar picket, step down to a smaller gauge (such as 13 or 14 ga) and add a ring shank rather than increasing diameter to gain grip. A blunt or semi-blunt point further reduces splitting.

The general rule: for thin pickets, decorative cedar, or any species prone to splitting, step down in gauge and add a deformed shank rather than growing the wire diameter. A smaller ring-shank nail will often outperform a larger smooth-shank nail with less splitting.

Shank Geometry: Where Withdrawal Resistance Is Actually Created

The shank is the single most under-specified property in fencing procurement, and it is the one that determines whether a fence loosens after two winters. Withdrawal resistance means resistance to the nail being pulled out along its axis exactly the load a wind-blown picket applies to its fasteners. A smooth ring shank might hold well initially, but in exterior cyclic exposure, wood fibers relax and the nail works loose. Deformed shanks mechanically lock into the wood fiber matrix.

Smooth shank

Lowest driving resistance, lowest withdrawal resistance. Acceptable only for concealed, non-cyclically loaded connections. For exterior fence boards exposed to wind, smooth shanks are rarely adequate.

Ring (annular) shank

Deformed rings along the shank engage wood fibers and typically deliver two to three times the withdrawal resistance of a smooth shank of the same diameter in common softwoods such as pine, fir, and spruce. This is the default choice for pickets, boards, and rails exposed to wind loading. In practice, this is the difference between a fence that rattles loose after two winters and one that remains tight after five.

Independent fastener testing used to support NDS design values shows that ring-shank nails in dense softwoods such as Southern Pine can achieve average withdrawal loads in the range of 150250 lb per inch of penetration for common gauges, compared to roughly 60100 lb/in for smooth-shank nails of the same diameter. These are research ranges, not design values: use the current NDS (Table 12N and commentary) for species-specific design numbers. The point of citing the ranges is to show the order-of-magnitude effect of shank geometry.

Helical / screw shank

A helical or screw shank distributes withdrawal resistance along a longer path and drives more smoothly than a ring shank in dense species. It is a good choice where assembly speed matters and splitting is a concern, and is common in coil nails for hardwood fencing and engineered framing.

Two practical cautions

First, ring-shank and helical nails are effectively permanent. Pulling them damages the surrounding wood fibers, so design for correct placement rather than removal. This is an advantage in a fenceit resists being pried apartbut it means misdriven nails are very difficult to extract cleanly, and prying attempts will mar the board. Use coil nailers with an adjustable depth stop and test the depth setting on scrap before running production.

Second, deformed shanks increase splitting pressure. If you move from smooth to ring shank in thin stock, verify with a sample run before committing to a full production batch. A simple field test: drive ten nails into a scrap piece of the actual board you intend to fasten, spacing them at the minimum distance from the edge you plan to use, and inspect for cracking. Repeat at the coldest temperature you expect in the production environment, because cold wood splits more readily.

Corrosion Protection: Read the Coating Spec, Not the Word Galvanized

Galvanized describes a family of processes with coating weights that differ by an order of magnitude. Service life correlates with , not with the trade label.