A traditional British unit of volume, used for beer. A pin is very different from a pint: it is equal to 1/8 barrel or 4.5 Imperial gallons (20.457 liters). There are 2 pins in a firkin. See also polypin (below)
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}