second string vs third string

second string

adj
  • Not as good; of a lower quality or condition. 

noun
  • A unit of players which is considered to have a secondary level of talent and which usually plays after the first string. 

third string

adj
  • Of a decidedly lower quality or condition. 

noun
  • A unit of players that plays behind the first and second strings; a junior varsity team. 

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