The Complete Handbook of Nails

Chapter 1: Understanding Nails

A nail is a metal fastener designed to hold two or more pieces of material together through friction and mechanical interlock. In its simplest form, it is a pointed shaft with a head at one end. Hammered or driven into material—most commonly wood—the nail remains in place because of the resistance of the surrounding material and the friction between the fastener and the material it penetrates.

This definition is accurate but incomplete. The reason nail selection matters, the reason nails fail, and the reason this handbook exists is that nail performance depends on a precise interaction between the nail's material composition, its geometry (length, diameter, head shape), its surface treatment, the type and grain direction of the material it fastens, the direction and magnitude of the load it carries, and the installation method used to drive it. Change any one variable, and performance changes—sometimes slightly, sometimes catastrophically.

Consider a straightforward task: fastening a two-by-four to a rim joist in a residential frame. A carpenter might specify a 16d common nail (three and one-half inches long, 0.162 inches in diameter), driven perpendicular to the grain. The load on that fastener is primarily shear—the force trying to slide the boards past each other parallel to the nail shaft. Shear capacity depends mainly on the nail's diameter and material strength. A larger-diameter nail, all else equal, resists shear better. Material matters too: a hardened steel nail resists shear differently than a softer, more ductile steel. Install the same