Fortunately for cyclists and mechanics, rear derailleur hanger threads have largely be standardized over the years to a 10mm x 1mm thread. While most frames are built with replaceable derailleurs hangers now, tapping damaged threads is less common, but generally still an option on intact replaceable hangers, and a must-have for frames with a built-in hanger. The Park Tool TAP-10 is the tool you need on hand for cutting fresh threads in the event of a cross-thread installation, poor manufacture, or perhaps excess finish paint.

Hardened carbon steel is machined into the thread tap style. The precision cutter must be used dead perfect for a properly aligned set of threads. Keep in mind that most replaceable derailleur hangers are made of soft aluminum. Any such hanger that has been bent should be replaced, not tapped. Sometimes an initial derailleur installation will go wrong, and in these cases the TAP-10 can be used to chase out the damaged threads. Some old or new steel frames will use an integrated, non-replaceable hanger and the TAP-10 will still effectively remedy thread issues here as well. Just remember that precision is required, and cutting fluid should always be used, no matter the material or application.