These 21mm wheel nuts are for use with 370Z or G37 Factory Sport wheels as the shank goes through the wheel applying the clamping pressure to the washer, not a conical seat. If you do not have these wheel nuts you are not getting enough thread engagement holding your sport wheels on which could be a safety hazard.
These wheel nuts are one piece unlike the factory nuts which have a Stainless Steel Cover over the steel nut which can deform over time and make installation / removal more difficult.