Well, it wouldn't be 1" metric because " is a symbol for inches and inches are not used in the metric system. I highly doubt that what you're looking at is a metric fitting. Although I have not much experience in SW equipment, I have a lot of experience in plumbing...having been one at one time, and also having managed a hardware store and been very involved in plumbing fixtures. I've never run across metric plumbing fittings except in the case of automobile fittings such as used on brake lines and such. Good luck, hope you get it figured out!!!