Master Flow GIC12 Rotary Turbine Ventilator, Steel | Permanently lubricated track system, upper and lower stainless steel ball bearings prevents metal-to-metal contact, encased to help prevent dirt, dust, sand and other foreign materials from damaging bearings for long life, less friction, smoother spin and wear resistance. Heavy-duty steel spider braces and case-hardened steel shaft for long-lasting strength/durability. Simple, mechanically-locked, two-piece head/base for faster, easier installation. Pre-punched bottom/crimped collar of one-piece base fits tighter, makes installation easier and allows for adjustability up to 12/12 pitch without removing turbine. Extra-large flashing and head with included bottom ring for easier installation and better weather protection. Double ribbed vanes, with convex top, direct even wind-driven rain away from the unit. Dade County/Texas Department of Insurance approved.