Oxygenating Stone (2 Micron) - 1/2 in. MPTThis is the stone we use in our FE390. It has a 2 micron stone and threads into a 1 2" MPT fitting and 3 8" diameter for O2 line. How long should I apply oxygen while transferring to the fermenter? We recommend you transfer half of your wort to your fermenter before applying inline oxygen (O2) to your wort transfer. If you apply O2 the whole time while transferring you are wasting O2.