[Dave at Pelican Parts]

OK, a look at the PET says that is the "wedge pin". BTW, the 911 shop manual seems to call it the "Wedge Pin (always replace)", which is a hint that you might not want to re-use it.

If you are replacing the ball joint and the pin, feel free to use heat on the pin. Also an air chisel. You may be able to get a press set up on it. If all else fails, cutting it may wind up being an option.

--DD