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.

This is the last hex wrench set you’ll ever need. With 15 Allen wrenches in standard measurement and 15 Allen wrenches in metric measurement, there won’t be a hex screw you won’t be able to ...

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 millimeters or 1/16-3/8 inch.