Once the control arms were back from the powder coater, and before I started reassembly, I wanted to make sure the internal threads were clear. I would imagine there was some surface rust at least in there.
I didn’t have a tap that big, and no way I was going to spend that kind of money, so I diced to make my own thread clearing tool from the old control arm ends. I ground some slots into a decent example of each size, used the torch to heat it up for a heat treat to harden it, and then was able to use it to clear all the internal threads. Worked like a charm.