In some applications a fastener can lock on to the rim of a threaded insert when inserted by a standard insertion mandrell. The insert may then wind back out with the mandrell when it is removed. DEEP DRIVE mandrels have a leading nose the same diameter as the root diameter of the insert which allows unflanged inserts to be driven below level. It also allows ganged inserts on longer insertion set screws for inserting multiple inserts.  Bear in mind however the external "threaded" fins on adjacent inserts on a mandrel may not seamlessly align in the same way the internal machine threads will.