I replaced some rusted balls in a pool cleaner that is no longer available on the market. The ball bearing is custom plastic but easy to open. Couldn't find balls anywhere near me so I'd be stuck buying a new pool cleaner that is about $350.00 as the cheapest you can find. These balls although understandably expensive saved the day and I'm hoping to stretch the service of the cleaner another year. If the other bearing fails I'll be buying a new set of these ceramic balls. I'm hoping these are impervious to all the chemicals they're exposed to.