They are like a normal nut at the bottom. But they drill out the top so the walls are very thin and then press a steel up into them. If you put any turning force at all too them they just mash in. Okay, well now they look like a rounded but smaller nut. Smash a new socket onto them. Turn it and they round over again. I just got a pair of vice-grip "nut out" (inverse of a screw/bolt out). After this fails (as I am expecting) what would you try? I am thinking two things: A) Weld a lug nut onto the remains of the current ones. B) Weld a cheap socket inside of the remains of the current one.
B while more expensive sounds a little more full proof. I can really get a good strong bead on the socket and not affect the drive hole.
BTW it is a 1985 K5 with I (believe) stock aluminum rims. I have the "wheel cover" off so I could get "that much" closer to the rim.
~TLGM