crosspiece vs hammer beam

crosspiece

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

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

hammer beam

noun
  • A member of a kind of roof truss (a hammer-beam truss), so framed as not to have a tiebeam at the top of the wall. Each principal has two hammer beams, which occupy the situation, and to some extent serve the purpose, of a tiebeam. 

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