The tight spaces and specific requirements of bike parts often call for specialist tools, even for some fixtures that seem like ordinary sizes. Brakes and derailleurs are a good example, and the Park Tool CBW-4 Open End Brake Wrenchwas made to address the issues. At just about 1/8" thick, the CBW-4 is stout enough for leverage, won't damage the nut or bolt it is being used on, and fits cleanly into tight spaces. Many common sized such nuts or bolts are metric 9mm and 11mm, so that is what this double-end wrench provides.

Made from steel, then nickel-plated for durability of the surface and tool edges, the CBW-4 is basically a one time purchase. Unless you misplace it or misuse it, you will have it forever, and for making adjustments to most caliper brakes and many derailleurs, nothing can easily replace it. Stamped markings remain clear for the life of the tool, and Park includes a hole for quick and easy hanging on a bench wall to keep it out of the way and ready for use.