I was in the garage warming my engine to do some tuning, when all of a sudden the fan flew off. I shut everything down and found that the fan, clutch, pulley, and flange was laying on the other side of the garage. Can anyone tell me how the flange is held on the shaft? I can't see any provisions for an internal faster or spot weld. Is it just a press fit? This is on a standard rotation Flow Kooler water pump.