cotter pin vs knag

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. 

knag

noun
  • A peg or hook for hanging something on 

  • A pointed rock or crag 

  • A small cask or barrel; a keg or noggin 

  • A knot in a piece of wood or the base of a branch 

  • A short spur or stiff projection from the trunk or branch of a tree, such as the stunted dead branch of a fir 

verb
  • To hang something on a peg 

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