An insertion tool is used to insert a threaded coil insert into a threaded opening of a support structure. The tool includes a rotatable mandrel body having an axial longitudinal passage and a projection slot. A plunger is disposed in the passage forward of a spring which urges the plunger forward. The plunger in turn urges a drive projection. A front end of the plunger includes an inclined surface that slidingly and inclinedly engages an inclined surface of the drive projection. The urging of the drive projection by the plunger along their respective inclined surfaces causes relative sliding movement of the drive projection so that the drive projection translates linearly through the projection slot in a direction perpendicular to the longitudinal passage.