Using this tool is the best way to ensure accurate derailleur alignment&44; & prevent shifting problems Screws directly into rear mech hanger threads Gauge bar pushes gauge rod against the rear wheel Measurements are taken at 6&44; 9&44; & 12 O Clock positions The tool is used to gently bend the mech hanger to the correct position Made from heavy gauge steel&44; with a chrome plated finish Updated over the longstanding DAG-1 the DAG-2 utilises a longer measuring pointer&44; longer threaded stud & a longer&44; narrower alignment boss to fit a wider variety of bikes