Impact drivable fastener

An impact drivable fastener to be driven into a thin metal article, said fastener comprising:

• a shank extending from a pointed tip to a shank end, wherein a surface formation comprising a plurality of sharply crested, helical ribs, said ribs extending along at least a part of said shank, and wherein a height of the ribs increases gradually from zero value at a start-of-taper position at one end of the formation to a maximum value at an end-of-taper position situated along the shank further from said pointed tip than is said start-of-taper position, and wherein said surface formation further comprises a like plurality of helical flutes respectively positioned between neighboring ribs, so that the ribs and flutes alternate around a circumference of the shank, and wherein a depth of the flutes increase gradually from zero value at said start-of-taper position to a maximum value at said end-of-taper position.