I'm helping a friend install rods with new ARP rod bolts on a 3.2 crank. We got to the first one, and after stretching only .05" we could barely move the nut, and then the box end wrench started rounding out the nut.
Threads and shafts were well greased with ARP assembly lube.
We used a 12mm 6 point box end wrench. The 12mm 12 point is too big, the 11mm 12 point box end fits about as well as the 12mm 6 point.
So, rather than use a 12mm as recommended, turns out an 11mm 12 point socket works, with frequent stretch measuring.
JB