Underneath the shower handle I've found this interesting design where there's a cover or shroud encapsulating the cartridge. The threading on it is interesting: the threading isn't required for the handle and there are two flat areas near the end. I'm guessing there's a special tool I should use to get access to the cartridge. (No, I don't think I'm referring to a cartridge puller.)
How would I find this tool? Or can anybody identify the manufacturer?