Abstract: A screw threaded fastener (103) has an elongate shank (122) with a drilling tip (104) at one end and a head (123) at the other end. A screw thread extends along at least a part of the length of the shank (122). The trailing flank (116) of the thread subtends an angle (B) relative to the axis (117) of the fastener which approaches 90° and is greater than the angle (C) subtended by the leading flank (115). The screw is for use in fixing sheets of material a1 to thin metal battens (5) and the angle between the trailing flank (116) and the adjacent thin metal section (18) of the batten (9), being reduced in comparison to a conventional thread form, lessens the distorting effect of the thread on the batten (9) under relatively high pull-out loads.