Abstract: Fan drive mechanism includes a fan plate rotatably mounted on a spindle by bearings having an outer race secured to the fan plate, an inner race mounted on the spindle, and ball bearings rotatably supporting the outer race on the inner race. A stop nut threaded on the spindle has a forward face engaging the inner race and a radially outwardly tapering conical surface tapering from the forward face. The conical surface catches the fan plate upon failure of the bearings and separation of the outer race from the inner race and controls the wobble of the fan plate while stopping its rotation, thereby preventing the fan plate from separating from the spindle.