If you think it was hard to get off, wait till you try to put i back on. They're pretty tight, I use a 6 inch piece of pipe that makes contact all the way around the lip to tap it on. I think its about 3 inches in diameter (you'll have to measure it). You can waste a half hour easy trying to tap it on without something that contacts it all the way around (or at least contacting opposite sides at once).