2 Micron Carbonating Stone with 1/4&quot; MFL Thread by Midwest Homebrewing and Winemaking Supplies. $34.99. Carbonate your beer just like the pros with this Carbonating Stone with 1/4&quot; MFL fitting. This Carbonating Stone will screw directly into that barbed swivel nut. Set your regulator to about 2 psi, and the gas will be forced through the millions of tiny pores in the stone, which dissolves the gas into the liquid. Your beer will be carbonated overnight. Note: To prevent the pore...