Corrugated board is classified according to the number of liners and mediums used: single face, single-wall, double-wall, triple-wall, and so on. The most common fluting types for board calipers are A, B, C, E, and F. These categories denote different flute sizes, based on height and frequency (distance between waves). Single walls are most found in A, B, and C-flutes, while BC is one of the most common double walls. The triple-wall, which is typically used for heavy-duty applications, varies depending on the manufacturer and location. Corrugated packaging comes in a variety of styles, shapes, and sizes depending on the application. There are international organizations that standardize construction.