Pin

Four and a half imperial gallons, being half a firkin, and the smallest standard cask in the British brewing trade.

The pin sits at the foot of the cask hierarchy, below the firkin and an eighth of a barrel. Its size is its purpose: thirty-six pints is about as much cask ale as a small gathering will drink before it goes off, since real ale once broached has only a few days of life. Microbreweries use pins for trial batches and beer festivals stock them for rarer brews, so the unit remains in everyday commercial use rather than surviving only in the record.