#friction_clutch  a clutch in which one part turns the other by the friction between them
  supertype:  #clutch.coupler  a coupling that connects or disconnects driving and driven parts of a driving mechanism
  subtype:  #cone_clutch__cone_friction_clutch  a friction clutch in which the frictional surfaces are cone-shaped
  subtype:  #disk_clutch  a friction clutch in which the frictional surfaces are disks
  subtype:  #slip_clutch__slip_friction_clutch  a friction clutch that will slip with the torque is too great

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