crosspiece vs purlin

crosspiece

noun
  • A bar or timber connecting two knightheads or two bitts; a timber over the windlass, with pins for belaying the running rigging. 

  • A horizontal or transverse beam or similar member that extends across or perpendicular to something. 

purlin

noun
  • A longitudinal structural member bridging two or more rafters of a roof. 

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