On frames with no derailleur hanger, a direct mount derailleur or derailleur with a hanger plate is used. These only fit bikes with horizontal dropouts, and are held in place by a small bolt and the rear wheel axle. These have now been effectively superseded by the derailleur hanger. Since a derailleur designed to be fitted to a separate hanger will be aligned lower on the bike than one that bolts directly onto the frame, it follows that a derailleur must be selected firstly with the mounting method in mind.