Types of Wood Screws

With the right wood screws in hand, even a relatively inexperienced carpenter can finish woodworking projects that are sturdy if not beautiful.
By Steve Maxwell
August/September 2010
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High-quality wood screws have serrated threads to dig into wood more easily with less chance of splitting.
PHOTO: STEVE MAXWELL
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Furniture isn’t what it used to be — and that’s not necessarily a bad thing. Traditionally, intricate, hand-wrought dovetails and other mechanical connections were necessary to supplement weak glues and simple nails. But today, there’s an easier way, and it all revolves around choosing the right types of wood screws (metal screws used to join wood, not screws made of wood) and hardware that works with them.

Metal wood screws are superior to nails because they have threads instead of smooth shanks like most nails. The threads let them grip the surrounding wood with much more power than nails, offering greater strength. Combine screws and glue, and you’ll have an amazingly strong wood joint. Wood screw threads are so effective, they draw the two halves of a joint together tightly, eliminating the need for glue clamps in a way nails can’t match.

You don’t need to be an experienced artisan to make great basic furniture with modern wood screws. Wood screws have become so strong, effective, inexpensive, and widely available they allow ordinary folks to build serviceable, attractive, and simple furniture. It’s a quiet revolution. Plus, because you can remove screws easily and reinstall them, they offer the leeway necessary to take several runs at woodworking success before you get it right. The key is understanding the hardware that’s available and how to use it.

Screws and Washers

Not all wood screws are created equal. Mailorder specialty suppliers (Lee Valley Tools is my favorite) are the best places to find the world’s greatest screws. Ordinary hardware-store deck screws are fine for many applications, but to get optimal results, you need a better-than-average screw.

Premium wood screws are sold under various brand names (my current favorite is Spax), and all offer a similar virtue: much better threads. You can tell simply by looking closely at them. The threads are thin and sharp, with serrated edges. This gives them the ability to burrow into wood with little or no splitting. It’s even possible to drive them into some kinds of hardwoods without drilling pilot holes.

No matter how easily screws are installed, or how well they hold, there’s still the problem of aesthetics. Wood screw heads are a bit of an eyesore, at least on their own. And countersinking (making a slightly larger hole, so the head of the screw goes beneath the surface of the wood) doesn’t help much either. What you need are better-looking heads.

The easiest and least expensive option for improving the appearance of bare screw heads involves the use of cup washers. Simply put one on a screw shank — domed side facing up — then install the screw as usual. The flat head of the wood screw nestles into the center of the cup washer, looking a lot better than it would alone. Cup washers look best with Phillips-, slot- and Torx-head screws, though regardless of the type of fastener you drive, there’s another benefit. Cup washers spread pressure over a much larger area than the screw head alone, creating a stronger wood joint because the screws have more surface area to rest on. Most cup washers are hollow, and the best are made of solid brass.

The only problem with cup washers is the way they sit — slightly above the wood surface. This looks a little too informal for some situations. Brass countersunk washers, on the other hand, are a more refined option that allows flat head wood screws to sit flush with surrounding wood. You’ll need to drill pockets of precise size and depth to contain countersunk washers, but the end product will look gorgeous with brass slot-head screws.

How to Hide Screw Heads

Sometimes hiding screw heads completely is best, and for this approach you can’t beat tapered wooden plugs. Buy them ready-made or cut your own using a simple drill press attachment. Don’t settle for ordinary cylindrical plugs; they don’t work nearly as well. Tapered plugs are more forgiving: They will snug themselves into holes quite nicely, even if they’re a little larger or smaller than they’re supposed to be.

Start by installing screws into counterbored pockets sized to fit the plugs you’ll insert later. Most tapered wooden plugs require a half-inch hole, followed by an eighth-inch-diameter hole for the screw shank. One nice thing about making your own plugs is you can use scraps from the same boards you’re using to build your project. Align the growth rings of these plugs with the rings of the surrounding wood, and the plug will nearly disappear after sanding and finishing.

If you’re using ready-made plugs, be aware there are two types. End-grain plugs are the most common, with growth rings visible on the tops of the plugs. Use these when you want plugs to be a prominent visual feature in your work, especially if you’ll be staining. Edge-grain plugs, on the other hand, are masters of disguise. They have the face of the board they were cut from oriented upwards, where they’ll be seen, so they’ll blend into the surrounding wood almost as well as plugs you milled yourself.

Almost all wood screws are used to bring simple butt joints together, and the results can be stronger than you think. Regardless of where you use them, wood screw butt joints look best if you offset the ends of adjoining parts a bit in the finished product. For best results, round the protruding ends of the joint with sandpaper or a rasp before assembly.

Three Types of Wood Screws

Fastening table legs to surrounding skirts? Securing knee braces on a post-and- beam structure? Anchoring a shelf under a workbench? Lag bolts are your answer. Despite their name, these aren’t bolts at all — at least not where it counts. They’re just big wood screws, though they do have a hex-shaped bolt head. Drive them with a socket wrench.

Ordinary deck screws are the cheapest wood screw option you’ll find, offering excellent performance in general applications. Premium wood screws look like regular deck screws, except for a few key features. The serrated threads of premium screws greatly reduce the tendency of wood to split, and the best include a dual-head design that accepts both Robertson (square hole in the head of the screws) and Phillips drivers.

Brass screws are classier than deck screws and lag bolts, but you need to be careful. Even the best brass screws are quite soft compared to steel ones. Predrilling proper sized pilot holes that are only slightly smaller than brass screw threads is key, especially in hardwood. If it takes more than a moderate amount of torque to drive a brass screw, stop and enlarge the pilot hole. If you don’t, even if the screw shank doesn’t break (and it probably will), the head will probably get mangled as your screwdriver slips.

Brass-pinned joints offer an exceptional option for joining wooden parts easily and beautifully, and it all starts with traditional flat head brass screws (the kind with a slot cut in the top for driving them). This type of screw head is designed for installation into predrilled and countersunk holes, but that’s not what you’ll do for this technique. Instead, after drilling a hole for the screw shank and threads, countersink a shallow pocket just half the depth required to contain the screw head. Your aim is to have the bottom of the driving slot sitting slightly higher than the surface of the wood, because you’ll grind the head of the screw flat so there’s no longer a slot in the screw head.

Use a hand-held belt sander with 80-grit sandpaper to level off the brass screw head so it’s even with the surrounding wood. Brass is soft, so leveling happens easily. Just be careful of heat. Lift the sander off the screw head after every couple seconds of contact to let the metal cool. There are never any sparks during this operation, but the brass will get hot enough to char the surrounding wood if you don’t allow cooling time. After you level the screw, sand the entire surface as you would normally, then apply a finish. It’s never been easier to produce great woodworking projects, so what are you waiting for? A pouch full of the right kind of screws and accessories will help you build like a pro.


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