If you’ve assembled IKEA furniture, you’ve used an Allen wrench. 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.
source https://lifehacker.com/how-to-buy-the-right-allen-wrench-set-because-you-need-1846767712