Screw for fibrous boards

A screw free of a drill bit portion and adapted for use with a fibrous board, comprising

• a shank portion which has a surface that is formed with a screw thread throughout the length of said shank portion, and which has a lower section formed with a flute at said surface of said shank portion, said flute extending from a tip of said shank portion and having a longitudinal length which is inclined with respect to a longitudinal axis of said shank portion, said flute being defined by a planar side wall which is inclined relative to said longitudinal axis, and a curved bottom, said planar side wall having a surface with screw thread portions that are disposed in a staggered arrangement in a direction receding from a direction of screw advancing rotation, said flute having a depth which decreases gradually from said tip of said shank portion, said flute having a maximum depth equal to radius of said shank portion, the longitudinal length of said flute forming an angle ranging from 12.degree. to 32.5.degree. with said longitudinal axis.