The three holes are found on all N2 clamping cones delivered from 2016 onwards. In combination with the separate special tool, they enable locking in the event the screw joint cannot, for any reason, be loosened unilaterally, e.g. if the bollard has not been removed for years. But: This 3-pin tool can only be used to lock the screw; it is not designed to tighten it.