Screws & Fasteners

The Right Screw Begins With The Metal
Steel screws represent the least expensive and most common type. They're strong, but like your car, they'll rust. That's why steel screws normally have a shiny plating of cadmium or zinc chromate. Unplated screws start with a blue hue, but eventually oxidize to a rust-brown color. When you need high strength plus corrosion resistance, opt for stainless-steel screws.

You might have to special order them (your hardware store can do that), as well as pay double the price, but they'll hold up outdoors. Steel case-hardened screws, originally developed for the manufacture of particleboard products, prove exceptionally tough because they've been heat-tempered. Case-hardened screws have a dull, flat-black finish and a skinny shank. They're used most often with a power screwdriver for driving into hardwood and particleboard.

For projects exposed to the weather, you'll want them galvanized or plated, at, of course, higher cost. With case-hardened screws, you can choose from two thread styles. Double-leads, or "hi-lo," have twin threads and work well in hardwoods. One-thread, single-lead styles are best for softwoods and particleboard because they hold. (See illustration below.)

Single-Lead Thread Double-Lead Thread
Exposed, brass screws can add a handsome accent, match brass hardware, and endure the elements. But, they're not as strong as steel, and may twist off if you drive them into too small a pilot hole. Their slots also will wear. However, in projects calling for oak, which contains a tannic acid that reacts with ferrous metal, woodworkers choose brass to avoid staining.

Aluminum screws corrode quickly in contact with dissimilar metals and twist off easier than brass if you apply too much muscle. So, they're an unlikely choice for woodworking, except when your project demands aluminum hardware.

Sorting Out Screw Sizes
Compared to other materials and fasteners, screw sizes are a breeze to figure out. Their gauge refers to shank diameter in a range from 0 (the smallest) to 24 (the largest). Gauge increases by .013", or about ¹⁄₆₄ ", in each increment. Screw lengths begin at ¹⁄₄ " and reach 4" or longer, though you'll probably stay in the middle range in your home woodworking.

To cover all possible applications, each length comes in three or more diameters. As a rule, the smaller the gauge of the screw, the thinner the wood you should use it in.

Head Styles You Can Drive Home
Different screw-head styles suit a divergence of woodworking needs and requirements. (See drawings above.)

Choose flathead screws for general assembly, where you will countersink or counterbore the screw before covering with putty or plugs. When a flush surface isn't important, or when you want a decorative effect, roundhead screws fill the bill.

You use ovalhead screws primarily to install hardware, such as cabinet hinges, because their shape matches the machined hole snugly.

Besides differing head styles, screws also come in choices of drive slots to match your tools (again, refer to the drawings on the opening page of this section).

Wood screws generally are sold by the box; those 4" and shorter packed in quantities of 100. Screws over 4" come in boxes containing 25 or 50, depending on their gauge and length. Most hardware dealers, of course, let you buy less than a box, but the individual price goes up.

To order wood screws from your hardware dealer or mail-order supplier, you must specify the type of head, type of slot, length, diameter (gauge), material, and finish. Abbreviations, such as FH, RH, OH, refer to flathead, roundhead, and ovalhead screws.

Think of a pilot hole as a custom-fitted binocular or gun case. As you can see in the drawing, it grips every contour of the screw, allowing the threads to bite and hold in the wood.When you drill a pilot hole, you're guided by the screw's dimensions: its length, the diameter of its shank, pilot (less threads), and head (for countersinking, or counterboring, if a plug will be used).

The easiest way to accomplish this is with a screw pilot, which drills all parts and configurations of the hole in one operation.

Finishing nails are thin, small-headed nails for installing molding and other interior trim. Usually you countersink the head and fill the hole with putty to make it invisible. When the smallest nails are too large, use wire nails, which have flat heads, and brads, with heads like finishing nails. Sizes designate the length and gauge.