Judging from the grind marks, it looks like jakeru was aiming to weld the inside corner where the side rail meets the bed(?) That's one massive heatsink but given the really small and well formed hole that Jim put into that block of aluminum with the 255ext, I think jakeru could have done that job with his new 255ext on Argon. The 255ext seemed to be able to put down a lot of localized heat quickly which is exactly what jakeru needed.