A tool set for implanting bone screws in a human spine, followed by the implantation of a rod into the bone screws includes end guide tools having flexible back wall flaps that receive opposite ends of the rod and intermediate guide tools that hold the rod in intermediate locations between the end guide tools. Both the end and intermediate guide tools include an attachment structure for operably connecting the guide tool to a bone screw. The attachment structure includes an undercut and/or recess so as to resist splaying and separation of the guide tool from an attached bone screw.