Allen Wrench

Sometimes spelled as alan wrench, the correct spelling is allen wrench and it is a necessity for your toolbox. A good set of metric allen wrenches is likely the most essential tool for modern bicycles. They are hexagonal rods of varying width (1mm – 10mm) designed to fit the many bolts on modern bikes from waterbottle cage, to headset, to crank bolts. If you find yourself working on bikes for a significant portion of your week a nice set of allen keys is a must. I like the L shaped ones with a nice rubber or plastic molded grip at the bend. For many a compact multi tool that includes the most common allen key sizes will be all that is required. Alternatives to allen wrenches include hexagonal rods of varying width by mm or even a good set of metric hex wrenches will do the trick. Just buy a set.