I had my sewer line cleaned and the plumber informed me that the previous owner had greased a rubber plug in place and that I should replace it with a threaded plug when I get a chance. It's hard to tell from the first picture, but the threads are significantly wider than any standard line used today (I've tried everything the store had to offer). I'm sure there is an exact jig somewhere, but I couldn't find it. This stub was exactly what I needed. Although the rubber threads on this connector are tighter than the threads on my cleaning, they still screw in until they fit snugly in the hole. I then used a deep end to tighten it until it was snug but not too tight. I went back to rock it a few times over the next few days and it wouldn't budge. I'm sure this thing will protect my sewer pipe for years to come.