fit together vs knock together

fit together

verb
  • To be able to be assembled in this way. 

  • To put the appropriate parts of (something) into a whole; to combine pieces that go together to create a finished object. 

knock together

verb
  • To assemble something quickly; to knock up. 

How often have the words fit together and knock together occurred in a corpus of books? (source: Google Ngram Viewer )