OHHH! that screw. All it does is hold the center, kinda-scalloped bolt (sorry, I can't think what the one in the middle of that clutch plate is called right now) at the location that you tightened, or loosened, it. It doesn't go deep at all. That whole screw, head to tip, is maybe a 1/4 inch if that. The round head of this little screw seats in one of the half-circle cutouts in the center bolt to hold it where it has been tightened. You may not want to put anything too long in place of it, and you'll want to make sure the head of the replacement screw is the same size as the half-circle cutouts of the center bolt.