A Hobson's joint or Hobson's coupling is a type of right-angle constant-velocity joint; rods bent 90° are able to transmit torque around a corner because they are all free to turn in their mounting holes in both legs of the coupling.[1][2]
Hobson's joints are used to make elbow engines, a novelty device,[1] but also for practical purposes in tools[3] and shaft-driven bicycle gearing.[citation needed]