#roller.wheel  a small wheel without spokes (as on a roller skate)
  supertype:  wheel  a simple machine consisting of a circular frame with spokes (or a solid disc) that can rotate on a shaft or axle (as in vehicles or other machines)
  subtype:  caster.roller  a pivoting roller attached to the bottom of furniture or trucks or portable machines to make them movable
  part of:  roller_skate  a shoe with pairs of rollers fixed to the sole

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