The Cold Block is designed to thread onto your faucet shank and pinch a glycol cold line between the "jaws" of the two pieces. This is an advanced optional component for the discerning kegerator builder. Whereas a block constructed from aluminum is very poor at retaining temperature due to high thermal conductivity, brass has a considerably lower thermal conductivity rating. This is a fancy way of meaning it will get cold and stay cold, keeping your beer chilled all the way from keg to faucet to glass. Note: some beers have more desirable flavor profiles at warmer temperatures, but if you're going for refreshing, there's few things better than a frosty pour. This is a set of 2.