I came in tonight for a cartridge of Nine Pound Hammer from Crystal Clear. I specifically said I was using an AiroPro, and was sold a "compatible" cartridge. I already have the screw on base, not the problem. They sold me a ceramic cartridge which has a blue metal ring around the base that makes it too large to seat into the battery. They refused to return or exchange the cartridge for one that is actually compatible after selling me this one as "compatible". I will not be returning to buy from this store as their only "solution" was for me to buy another battery out of my own pocket.