split pin vs thumbtack

split pin

noun
  • A stationery fastener that is inserted into punched holes in a stack of paper before being bent to secure them. 

  • A metal fastener with two tines, the ends of which project through an object being fastened and are bent back to hold it in place. 

thumbtack

noun
  • A small nail-like tack with a slightly rounded head that can be pressed into place with light pressure from the thumb; used for hanging light articles on a wall or noticeboard. 

verb
  • To fix or attach something with a thumbtack. 

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