"Barrel nuts are banned"
Possibly because there is ambiguity in what a barrel nut is. " The barrel nut is a round slug, or formed sheet metal part with threads perpendicular to the length of the nut."
In other words, the thread goes across the round bit, not down the length.
However the barrel nut in karting was a long nut, usually round with a blind thread, ie the hole did not go all the way through, with the blind end given a hexagonal shape to fit a standard socket.
Long nuts often act as locking nuts because small distortions in the pitch of the thread take up any clearances between nut and stud.
They do have a problem that if the length of the nut extension is shorter than the exposed length of the stud, then the stud bottomed out and although the nut felt as if it was does up, the wheel was actually loose. Since the nut thread was blind, it could get shortened by debris getting into the hole and not being cleared before the nut was used. This was demonstrated to me by someone who used a bit of Blutak in the hole then turned up a bolt against it. The bolt only went half way in (it was a big piece of Blutak) but tightened up solidly.
There is no easy way to check that the hole in the nut is deep enough, apart from screwing the nut onto an exposed thread, and measuring the distance. With a normal through nut one can see that the stud comes through the nut and has a minimum of three turns clear. Indeed I have been sent away from scrutineering because my nuts did not have the three turns showing. I had two choices, turn the studs around (they have a long end and a short end, the long end should be out, I had the short end out) or fit wheels with a thinner centre, I was using Mag alloys with thick centres.
So safety in tightening wheels: 1) check the state of the rim and the locator. 2) make sure the wheel is properly homed before tightening 3) make sure you are using the appropriate measure of tightening. This is either a torque wrench or the angle of nut method (ie, turn the nut up to firm, then turn it a certain angle to apply the right presure to the joint) 4) Repeatedly tightening /loosening nuts makes them unreliable. It wears the threads and alters the friction qualities so torque or angle no longer = tight. Throw them away periodically. 5) you should have at least 2 to 3 threads showing above the nut. 6) If you are using a standard impact driver, know what it is set to. 7) be careful starting the nut, an impact driver will cross thread a nut without you even noticing.
8) Don't watch what I do, do as I tell you.
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