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         Crank gear: mechanism comprised 
          mainly of pedals, cranks and a chain wheel that drives a bicycle. 
          Frame: chassis of a bicycle. 
          Cone: roller bearing. 
          Fixed cup: metal plate covering the ball bearings. 
          Chain wheel: support that holds a disk clutch. 
          Pedal: foot-operated system used to propel a bicycle. 
          Crank arm: arm perpendicular to an axle, used to give it circular 
          motion. 
          Ball bearings: ball-bearing mechanism used to reduce friction 
          between pieces rolling on each other. 
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