Great for 30 gallons. Take your time with the initial thread, because you are screwing metal into plastic. At first I had problems with cross-threading. If this happens, stop and position the barrel so that the hole is level with your line of sight. Align the cap so that the flange on the cap is parallel to the edge of the hole, but don't press on the cap, touch it. Do not start rotating until they are parallel to each other. The lid will eventually grab and screw tight. A little silicone grease helps a lot.