hand truck vs stack truck

hand truck

noun
  • Synonym of pallet jack 

  • An L-shaped box-moving handcart with handles at one end, wheels at the base, with a small ledge to set objects on, flat against the floor when the hand-truck is upright. It makes otherwise bulky and heavy objects easier to move. 

stack truck

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