Hex wrenches, also known as Allen keys, are the tools you use to screw and unscrew fasteners that have a hexagonal recess (as opposed to a Phillips or flathead recess). Hex screws are commonly ...

Allen screws made from weak metals strip quickly, and using the wrong size Allen wrenches/hex keys can also damage them. Regardless of the reason, it's no fun trying to remove a stripped Allen screw.