The use I purchased this mud pan for is a bit unconventional. My furnace requires a 20 X 24 filter. Unfortunately, it sinks completely into the slot and takes forever to get it out so I but the 20 X 25. This leaves an inch sticking out which I had been covering with a couple of 2 X 4's, not ideal. This mud pan will completely cover the top of the filter that sticks out after putting some magnetic tape down to complete the seal. Then, if I ever do need a mud pan of this size, it's waiting for me.