Nope - not serrated. Some guy did a real good YouTube vid on this replacement.
I used a air hammer chisel (with a nut on the end of that bolt), 3 LBS hammer, impact on the bolt head, etc. NOTHING.
To remove the half shaft, the axle nut needs to come off, just broke my 1/2" breaker bar that I've had for 25+ years. That was after heating the nut up.
Gonna be a long job and a few broken tools.
How does Hank work on these salt fested cars?