12 in. Galvanized Internally Braced Turbine Head in MillThe GAF Master Flow internally braced turbines are efficient, easy to install venting options for your roof. They allow heat and moisture laden air to escape your attic, helping to extend the life of your roof. They are designed with upper and lower steel ball bearing systems for years of trouble free operation. Dual bearing system with encased design helps to prevent dirt, dust, sand, and other foreign materials from damaging the bearing, resulting