An impact drivable fastener, suitable for fastening sheet metal articles, includes a shank extending from a tip (10) at one end, which tip is adapted to be driven through a metal sheet, and a head (10) at the other end. A large pitch multi-start thread formation (11), 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.