12". Constructed with components designed to meet or exceed industry specifications and standards. Co-polymer bearing system for quiet, long-lasting, and smooth operation. Raceways fully machined to deliver low drag and quiet operation. Tested to ensure durability and performance in extreme temperatures and high winds. Adjustable to a 6/12 pitch. 2 turbines will ventilate 1300 sq. ft. Limited lifetime warranty. Galvanized internally braced.