Apparatus for making foundation pilings includes a lead section with screw threads, at least one extension section, and a bit carried by the first of the extension sections. The bit slides onto the first, lower end of the extension section and is operable to compress the soil laterally to the extension sections and form a lateral groove in the soil. Grout fills the annular region of the hole bored by the apparatus including the grooves for lateral stability. Each extension section is formed to fit into the next one and to be secured to it by lateral bolts. The bolt heads prevent the bit from moving vertically as the lead section advances into the soil. Bits may be added to increase the size of the opening bored.