cotter pin vs pinball machine

cotter pin

noun
  • A pin or wedge inserted through a slot to hold machine parts together; a cotter. 

  • A split pin, the ends of which project through an object being fastened and are bent back to hold it in place. 

pinball machine

noun
  • A machine specially built to be used to play games of pinball. 

How often have the words cotter pin and pinball machine occurred in a corpus of books? (source: Google Ngram Viewer )