The name given to the “pie crust” indentations around the cap of pillar boxes; a design feature said to facilitate rainwater run-off. Different foundries have different styles of flutes. Only three types of traditional pillar box do not have fluting; the Type D (large) and Type E (small) oval boxes of 1931 that incorporate a stamp vending machine, and the “Nigerian” Type B boxes of 1979/80, with the cap and body cast as one piece.