I removed the first of the old fixtures and discovered that the existing fixture box was recessed behind the brick so that the supplied mounting screws for the new fixture weren't long enough. So I took the headless screw that the manufacturer had supplied off to the hardware store where I'd bought the fixtures. The lighting guy sent me to hardware. The hardware guys stared at it, sold me some #6 screws and a bolt cutter, and sent me home.
This would have been great had a number six screw actually been what would fit in the mounting plate. I inspected the old mounting hardware and realized that I'd threaded a slightly larger screw through from the rear. This made sense and suggested that I really didn't need to cut off the screw head.
So daisy_knotwise, Katie, Julie, and I packed off to lunch and then back to the hardware store. I returned all of the previous purchase, then walked back to the hardware department with the mounting hardware. I handed it to the guy who had sold me the #6 screw before, informing him that a #6 was too small.
This time, he tested it with a #8 screw -- which fit fine -- and I bought a packet of longer screws than the ones that I'd used the last time I mounted an outdoor fixture on this box, since the screws that were in the old mount were clearly too short. I came home, mounted the fixture with no further difficulty, and everything was fine.
The next fixture box stuck out slightly from the wall. This meant that the screws that were supplied with the light were more than long enough, but I ended up having to cut and insert a wood shim to get it to hang right.
Then I went to hang the last light. I was almost done. I just had to put the last little round black nut on the outside. And I had to do it left handed. The one thing I didn't want to do was -- Oops!
Was to drop the little round black nut on the black dirt behind the holly bushes. *sigh*
I called Gretchen for help, because she's better close to the ground than I am. After about two minutes, she located the missing nut. I twisted it on tight, went to the basement, turned the circuit breakers back on.
And there was light!