You already own a brake adjuster tool!

Sure, you could go out and buy a brake adjuster tool. But where's the fun in that? Instead, try this little trick I found on the Internet somewhere. I'd love to give credit to the person who thought this up, but I'm afraid I don't know who that is. To whomever it is, "Ta!"

Here's what you do: Get a largish 'L'-shaped Allen wrench (I used a 5/16", but nearly any size will do). Get a 1/4" drive socket that's the same size. Put the hex portion of the socket on the short leg of the Allen wrench. Put the square-drive end of the socket on the adjuster stud. Et voilà! -- brake tool!