I have a leaky faucet in our bathroom bathtub. I have removed the knob and what appears to be an extension stem and have come to what i assume is the cartridge that needs replaced. I have not been able to find the correct socket size to get a clean fit to torque the cartridge and want to avoid stripping it. It seem like it is really stuck. I purchased a shower valve wrench set and the closest size that fit was 31/32, just a tad too big and 29/32 just a tad too small. I couldn't find a 15/16. One side of the cartridge looks like it will fit a socket, the other side is rounded. Maybe i need a special tool? Does anybody know, from the picture, what brand or type this may be? Any help is most appreciated.