These water bottles and holders are great - everything Masons Cavies said they are. I have a few guinea pigs that have been very fond of pulling my glass bottles with the wire holders down. They'll have to work very hard to pull these down! Buttercup Pet Products was wonderful in helping me place my order - I'm from Maine in the US. I have 3 jumbo sized Living World cages, and the holders were very easy to install - I thought I might need help holding the components in place, but I was able to do all 3 by myself in just a few minutes. For US customers who are used to ounces instead of metric, I'd recommend ordering the Large bottles - they hold about 12 ounces of water at the 400 ml mark (and it goes to 500 ml). The Midi size only holds about 8 ounces. And the guinea pig who gives me the most trouble with water bottles was the first one to try it out - the tricolor one in the cage with the strawberry print bed.