I'll look at the others when I refill it and put the pressure tester on it. I'm thinking it's kind of a one-off deal, since the one that was leaking was a factory block heater style plug. Brass with a rubber o-ring, and a compression/pull-in screw on the outside similar to a molly bolt that you'd use to hang a picture on drywall. When I looked at all of them the other day trying to find the leak, they were all dry, but I'll recheck tomorrow. The coolant was still green when I drained it, with only a hint of brown.