How to Buy the Right Allen Key Set (Because You Need One)

If you’ve assembled IKEA furniture, you’ve used an Allen key. These slim, L-shaped contraptions are often the only tool included in the packaging, even when you’ll need others to finish the job. There’s a good reason for this: Most people don’t own Allen wrenches, and when you need one, nothing else will do.

For some reason, Allen keys — which are also called hex keys, Allen wrenches, or hex wrenches — aren’t included in many basic toolkits, despite being inexpensive and taking up basically zero space. Their hexagonal heads (hence the “hex”) are used to loosen and tighten bolts and screws with hexagonal sockets, which are found in everything from bikes to furniture to certain types of electronics. If you don’t already own stuff that’s held together with hex socket screws, it’s only a matter of time until you do — and this time it might not come with its own Allen wrench. In other words, you should definitely buy your own. Here’s how to choose a set of wrenches.

Choose your size: Metric vs. imperial

Allen keys are sold in sets, with a variety of sizes designed to fit different sockets. You can buy metric or imperial wrenches, depending on what kind of screws or bolts you’re working with. Most sets offer sizes ranging from 1-10 millimetres.

If you only buy one set of wrenches, make it metric. The vast majority of manufacturers in the world use the metric system, so metric wrenches are a must for basic repairs. But if you live in the U.S., it can’t hurt to have an imperial set, too, because that’s the system used for most screws and bolts sold in U.S. hardware stores. Imperial and metric wrenches aren’t really interchangeable, so owning a set of each is smart, not redundant — and besides, they don’t take up much room in a toolbox.

Choose your shape: Ball end vs. flat

Once you’ve settled on buying metric or imperial wrenches (or a set of each), you’ll need to further narrow down your options by shape. Some Allen keys are flat on both ends, while others have a “ball end,” which is pretty much exactly what it sounds like. Both types do the same job, but ball end wrenches are a little more versatile because the rounded shape is easier to manoeuvre in tight spaces. You can get a hard-to-reach screw started with the ball end, then switch to the flat end to finish the job.

Even if you’ve never needed an Allen wrench that didn’t come as a package deal, you almost certainly will at some point. Hex socket screws are in everything — when one of them goes rogue, you’ll be glad to have your very own set of wrenches.