I have a drum trap/cleanout in the floor of my 1929-30 house in Baltimore, and I'd like to replace the cover with something a little better looking than the original. A neighbor has one with a flange around it that covers up the raw edges of the tile around the trap, but they didn't buy it, the previous owners did, so they don't know where it came from. My cover has the number 3 on it, but it does not measure exactly 3 inches across - more like 3 1/8 on the inside of the threads in the cover, and more like 3 1/4 outside dimensions when it's screwed down to the floor. Is this a standard 3 inch size? It also has some other numbers on it, 25 628. Is this one of those things that is nonstandard and impossible to replace? Thanks for any expertise on this thing!