I haven't seen them or used them on dirt, maybe they only make them on the 8mm metric thread. Again the way they lock is because the thread is not round, but oval. I don't use an impact with my asphalt sprint karts, maybe that would mess them up I don't know, but on most European karts people rarely use power tools for wheels nuts. You don't usually have to change tires so often as with dirt oval karts, especially if you have a limited number of sets you can use for a race. Obviously when racing on top level you don't save on wheel nuts, and you replace them very often like you should on any kind of kart.
