cap of maintenance vs fedora

cap of maintenance

noun
  • A ceremonial cap of crimson velvet lined with ermine, worn or carried as a sign of nobility or special honour. 

fedora

noun
  • A felt hat with a fairly low, creased crown with a brim that can be turned up or down. 

How often have the words cap of maintenance and fedora occurred in a corpus of books? (source: Google Ngram Viewer )