#piston_ring  seal consisting of a split metal ring that seals the gap between a piston and the cylinder wall
  supertype:  seal.holdfast  fastener that provides a tight and perfect closure
  part of:  piston__plunger  mechanical device that has a plunging or thrusting motion
     part of:  reciprocating_engine__reciprocatingengine  an internal-combustion engine in which the crankshaft is turned by pistons moving up and down in cylinders

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