I am trying to replace my shower head and the threads are seized from the shower arm to the connection to the shower head. I have used WD40 several times to no avail.
HELP.

Not sure WD40 is supposed to be particularly good on seized parts. It's more of a cleaner with a bit of lubricant in my experience.

These are both copper parts?

Chrome plated something, maybe copper. I will try some penetrating oil

Thanks

Apply more pressure. It will go...

Put a 14" pipe wrench on the shower head and turn it it counterclockwise out. Since the threads are chrome over brass there can be no rust that's locking it in place. Put a little muscle behind it and don't screw it in so tight next time. Good lucki. Tom