Single-piece 12 flute, mandrel-formed, aluminum tapered shaft 7Ó round (178 mm) welded top and bottom to a cast-aluminum anchor plate. After tapering, forming and welding, the entire shaftassembly is heat-treated to T6 temper. A 4Ó by 7Ó (102 by 178 mm) maintenance opening is complete with aluminum cover and copper ground lug.