Staring at a wall of screws can make you go a little crazy. A piece of wood? Grab some wood screws. Drywall anchors? Get a roll of those. But do you know what you’re grabbing? There are lots of tiny differences between each screw profile, and it’s hard to understand why they has such odd names.
That’s why it’s tempting to think of every screw as being exactly the same; but then you strip out the head and tear through the wood. Or maybe you use the wrong screw for the job and your joint give out on you later. Knowing how the screw works will give you the confidence needed to put together something that looks like it was done professionally. And more importantly, the joint hold together.
How to Pick the Right Screw
When we break screws down visually, there are two components to consider; the head profile and the drive recess. Why do these matter? The head describes what shape the screw take when it sits against the material. The drive describes how much force you can use to tighten it before the metal strips.
Novices only consider drive type. They’ll take the first Phillips bit handy. But the head style ultimately affects the strength and final look of the project. For example, if I use a flat head screw then I need to make sure I have a precise countersink cut in the wood. Otherwise, the screw will be sitting proud of the wood’s surface which just makes everything ugly.
A bugle head (which is the right choice for drywall) becomes its own countersink. It flares outward to spread out pressure and prevent tearing the paper face off. As the chart points out, not all heads that stick up are alike. Round and pan heads both stick up but they leave very different footprints.
The bearing surface on a pan head is larger than a round head which is why it works better on thin sheet metal where you don’t want the screw to pull through. Take the concept one step farther with a truss head. You get even more footprint with a low profile, wide head. It is perfect for soft material when you don’t want your screw digging in too deep.
Maximum surface area will help keep your screw exactly where you want it. It is about physics, not just looks. Apply torque and what happens? Force go through the head. Concentrate that force at a small contact point or spread it out by using a wide head.
And then there’s the drive type to consider. According to the infographic, the old-school Phillips cross is good for lower torque applications while the hex and Torx types provides greater torque without the potential cam-out. In fact, that was the intent behind the Phillips design, to slip free once it gets too tight for hand tightening, though this is annoying if you are using a power tool.
If you’re constructing something with longevity like a piece of furnitures or a structure like a frame or work bench, going with a square or a six-lobe Torx drive will help things stay connected. Hex sockets found on many lag bolts is made for applying huge amounts of torque. That’s why they dominate in heavy duty and outdoor construction.
Another metric detail is the countersinks. Metric screws typically have a ninety degree countersink and our US inch size flat heads are usually eighty two degree. So in theory your typical countersink bit for US will not fit and seat metric screws quite flush. It is a small thing, but it is one of those things that makes a difference if you want something to look clean.
Maybe you’ll spend a half an hour or maybe even ten minutes trying to make a screw sit right. Then after you do you notice it’s angled off by eight degrees. So which screw do you pick? It is not necessarily about picking a number from the catalog. It is about knowing how shape of the screw relates to the material. We need an efficient way to transmit our force so the screw holds the load without damaging surface where its head sits.
The next time you grab a screw: stop for a moment. Examine its profile. Think through the thickness of material it will penetrate. And pick the right tool for the task, instead of just the screw that’s lying on your workbench. Those little geometry decisions make all the difference between a wobbly shelf or a solid one.
Understanding them makes selecting screws a deliberate exercise, instead of a maddening struggle through the hardware aisle. That way, every joint you create has strength equal to its appearance.
Actually, it could of been easier if we had better guides. I should of mentioned that earlier too.
