Crews only requested the prop to be held, during it's engine start-if there was a wind present that caused the prop to rotate in the opposite direction, after the prop-brake was released. The prop (if unrestrained and the wind was strong enough), could pick up a considerable rotation speed in the wrong direction and then cause considerable bearing load and adverse effects of gas temps over the turbine-before rotating in the intended direction. The procedure was to hold a blade between finger and thumb until the turbine began to drive the prop shaft-there was no "Clunk" as suggested by some further on, in this article, the clunk was the prop brake disengaging. The blade then moved ever so gently out of the holder's finger/thumb.