A faucet adapter is a very small and simple piece of equipment that can make a huge difference in homebrewing. It is designed for one purpose, which is to allow the attachment of garden hose threads (GHT) to a standard kitchen faucet.
Most homebrewing equipment that is designed to attach to a water supply is built for use with utility sinks or fittings that have a male thread with a 1-1/16” outer diameter (OD), like that of a standard GHT fitting.
Unfortunately, most indoor kitchen faucets are equipped with a smaller female thread to allow for connection of an aerator. The faucet adapter bridges the gap by syncing up the two different thread types.
There are two big ways in which the faucet adapter can save you a lot of hassle in homebrewing: chilling wort and cleaning bottles, carboys and tubing.