The nut spec is M20, 1.5. I bought a couple of standard hex nuts from Amazon, stainless steel, no outer metal flange. I'll see how it goes. The stock nut seized just as the metal flange reached the end of the axle when unscrewing. There was no corrosion or rust on the axle threads. I don't think anti-seize would have helped here, and I had never taken the nut all the way off before, only loosened it to adjust the chain. I do agree that the torque spec of 100Nm (74 lb-ft) is high. I went with 72Nm this time.The nuts are fine, but should be put on with some anti-seize on the threads.
The torque spec for the gen 1s was too high, I don't know about the 3rd gens.