The second item I had success
with was the 5/8" heater nipple that is a press fit into the engine,
underneath the oil filter. Mine was missing from my engine. I tried to
find a new one, with no success. Finally, Mazdatrix sent a used one,
but when I put a micrometer to it, it was considerably out of round
(probably caused during removal from the casting).
I found at our local CarQuest
auto parts store, a steel 5/8" hose barb to a 1/2" NPT male fitting. I
just put it in a lathe, and turned the 1/2" NPT threaded area down to
17 mm, or .160 inches. In the picture, you will see the longer original
piece, as well as the new, slightly shorter nipple.