When my car was subject to a nut and bolt restoration it looks like Kevin sprayed the whole axle including brake drums with black two pack black lacquer, and as Richard typed above they still look unmarked after circa 20k miles or more, and over a period of 20 years..?
If using a Hammerite product, then it might be more suitable to use one of the colours in the Smoothrite range, as the hammered finish can have issues in terms of appearance and coverage...? I have used Smoothrite with success on engine blocks and suspension components of my sports cars over the years with a degree of success.
Good luck in your choices..
