This unique Jug- Growler filler has a metal fitting that fits into most standard American beer faucets. The other end has a hose that goes into growler for filling. Perfect and easy solution to fill your growlers from bottom up. *Fits well on most standard American faucets. Some faucets have irregular or non standard size spout and the growler filler may not fit well on those. It will not fit on Perlick brand faucets as the spout is slightly smaller in size. If you have Perlick faucets, please purchase the ones specifically made for those. 12mm Diameter - Fits most standard Beer faucets.