Statistical Analysis of Measurement Errors

A screw anchor for penetration and holding in soft soil comprising an elongated shank rotatable about its longitudinal axis and having a lower end adapted to penetrate into the earth upon rotation. A helical flight is secured to the shank for holding engagement in the earth and includes a crowned upper surface extending outwardly of the shank and sloping downwardly adjacent the outer edge thereof, thereby increasing the holding strength of the flight by providing a larger, frustoconical, shear area in the soil rather than a smaller cylindrical shear area, as with conventional anchors.