It’s summer, and the weekend air is full of the sound of sawing, hammering and (occasionally) cursing. Yes, it’s time to break out the tools and build that deck, fix that roof, install that new door–and whatever your renovation plans, you’ll probably use either nails or screws in abundance.
The nail is the simplest and oldest fastener in common use today, but the nail as we know it is a product of the Industrial Revolution. Until the late 18th century, every nail had to be individually forged from a square rod by a blacksmith. “Wrought nails” were so expensive that houses were still mostly assembled with wooden pegs, and old building were often burned down just so their nails could be salvaged.
By about 1785, hand-operated nail-making machines been invented that cut nails from flat bars or sheets of iron. The price of nails began to fall. It fell further after 1883, when the first mass-produced steel-cut nails were made at the Riverside Ironworks in Wheeling, West Virginia, using steam-powered machinery.
But steam power was also applied to an 1835 French invention that simply clipped nails from spools of steel wire. By the 1900s, these wire nails had almost eliminated cut nails, and they’re what we still use today.
A nail works by driving apart the fibers of the wood into which it is being driven. The fibers’ natural elasticity makes them attempt to spring back into place, so they immediately grip the nail tightly.
A round, needle-sharp point is most efficient at driving wood fibers apart, but it’s seldom used–it’s so good at forcing apart wood fibers that it tends to split the board into which it’s driven. Blunt-tipped nails avoid splitting, but they don’t hold as well because they tend to crush the wood fibers rather than spread them. As a result, most nails have a diamond-shaped point, an effective compromise.
Nails come in all shapes and sizes, depending on their purpose. Finishing nails have almost no head, so they can be hidden in trim work; upholstery nails have very broad, decorative heads. Most nails are round and smooth, but square nails are used for nailing into concrete, and ridged or spiral-twisted nails are used when a very strong, permanent grip is required. Nails can be made from ordinary steel, or galvanized (coated with zinc) to reduce corrosion. (Aluminum, stainless steel, copper and bronze are sometimes when corrosion is of particular concern.)
The measurement unit for nails is the “penny,” abbreviated “d.” It once referred to the price of a hundred nails of that size, but now it refers to the length. A 2d nail is 2.5 centimetres long; a 60d nail is 15 centimetres long.
As wood dries and buildings vibrate and twist due to wind or the slow shifting of their foundations, nails eventually loosen in their holes. Yet houses generally remain standing for decades That’s only possible because so many nails are used: an average-sized wood-frame house contains between 20,000 and 30,000.
When you need more grip than nails can provide, you’ll probably turn to the screw: a cylinder with a spiral ridge, called a thread, running around it. This thread is essentially an inclined plane, a basic machine. As a screw is driven in, this inclined plane applies the force of the turning screwdriver to moving the screw further and further into the wood. The spread wood fibers then grip the screw tightly, just as they do nails.
Screws come in a huge variety of thread angles, pitches (the distance between the crest of one thread and the next) and core diameter (the diameter of the cylinder around which the thread runs). A high thread angle–a more sharply inclined plane–gives a screw greater penetrating power, so it can be driven into wood more aggressively. The pitch helps determine the holding power of the screw; in a thin component, you want a small-pitched screw so that there’s lots of thread holding it in place. Core diameter works much the same as in nails: a fatter screw will grip better, but it’s also more likely to split the wood.
Whether you choose a nail or a screw to hold together your latest home project, as you work you will share certain basic concerns with all the million of other people who have built things over the past two centuries: you’ll hope the thing will stay together when it’s finished, and you’ll really hope you don’t hit your thumb with the–
Yeeeeowww!
Some things never change.
