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This fits perfectly on our 10 inch gerbil tank. It's got a little slack, so it isn't too snug, but it's also not too loose. I'm not sure how this would work with other animals, but our gerbils can be frisky sometimes. It may be fine as a stand-alone with certain other animals, but you will definitely need to buy clips to hold it on if you are buying this for your gerbils. Ours occasionally jump up and use the air holes like monkey bars, or even get on all fours and walk upside down on it for a few seconds. They eventually jumped up hard enough to shoot a clip off a couple of times, so we got nervous and put a small, yet heavy notepad on top for extra security. There have been no problems since then.