an impact drivable fastener , suitable for fastening sheet metal articles , includes a shank extending from a tip at one end , which tip is adapted to be driven through a metal sheet , and a head at the other end . a large pitch multi - start thread formation , including ribs separated by flutes , is formed on a part of the shank . the depth of the flutes and the height of the ribs increases uniformly from zero at the starting end of the formation nearer to the tip to maximum values at a position adjacent the head .