steering coupler removal

I've been trying to remove and replace my power steering gear box and I am having trouble getting the coupler pin drilled out and even drive it out. Does anyone know what size the pin is so I am using the right size bit. Ive never seen anything so difficult in my lifetime to remove even with pb blasterand all.

I know it! Had this problem myself. Once you get the correct "chisel" don't know the exact name, but it is 5/16. Make sure you are pounding the right way, it only comes out one way.