Oxygen stone to aerate wort for faster and better yeast production. 0.5 micron barbed connection.
IT IS IMPORTANT TO HANDLE THE OXYGEN STONE ONLY BY IT'S STEM. OILS FROM YOUR SKIN CAN PLUG THE PORES. If this happens you should boil the stone in water for 1 - 3 minutes to remove the oils, then sanitize the stone with a sanitizer such as Star San.