Removal of 6" Jinma Chipper knives?

[cordwood]

I am trying to remove the knives from my chipper and reverse them. The screws holding them down seem to require a 4.5 mm hex bit, which is an unusual size. I only have a cheap t-handle wrench in 4.5mm and can't seem to get enough force on the screws to break them loose. I've tried heating the screws with my MAPP torch with no success. I'll give them a spray with PB blaster, but it doesn't look like I will have much luck actually getting any solvent onto the threads. Does anyone have any tips or tricks for loosening those screws?

[quicksandfarmer]

There are nuts on the other ends of those screws. The hex head is just for keeping it from spinning while you turn the other end with a wrench.