Is there a universal rear mech derailleur hanger?

Short answer: No!

Long answer: There’s at least 2 ‘universal’ rear mech / derailleur hangers, but they are not suitable for every bike

  • There is emergency mech hanger which can be used on most bikes with a quick release (QR) hub and axle. This hanger might be useful if you often ride with others and want to have a spare if others in your group have a broken hanger. It’s meant as a temporary hanger just to get you home, and it’s unlikely you’ll be able to use the full range of gears on your cassette – however it’s better than walking home!