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Allen Wrench
A solid hexagonal bar, usually "L" shaped for leverage, that fits into the hollow hexagonal hole of an Allen bolt head.
This tool is sometimes confusingly called a "hex wrench," "Allen key" or "hex key."
The terms involving "hex" can be confusing, because normal cap screws also commonly have (external) hexagonal wrench flats, and hexagonal box or socket wrenches fit them.
I prefer not to use the term "key" for such a tool. Many languages use the same word for "wrench" and "key", but I believe that it is one of the richnesses of the American English language that it makes this distinction. Since "wrench" is not used in this context in British usage, "Allen key" is acceptable if the appropriate accent is used.
One of the nice things about Allen wrenches is that they can be sharpened very easily, just grind the worn part off with a bench grinder, and an old, tired Allen wrench becomes as good as new, so long as you don't let it get too hot while you are grinding it.
