bitstock vs drill bit

bitstock

noun
  • A hand tool consisting of a crank which holds a fitted rotating drill bit tip, designed to bore holes in rigid materials, by cutting a disc in a spiral fashion. 

drill bit

noun
  • A twist drill. 

  • Any other style of cutter, for example a spade drill, that is rotated and fed in a similar manner as a twist drill to of cut a hole in metal, wood or other materials. 

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