I am replacing my bathtub faucet cartridge, which is made by Moen. I
am not sure the original part number, but the Moen website has a handy
lookup menu, which got me close... The cartridge is either part number
1200 or 1225. I can't narrow it down further than that without
pulling out the old one.

Does anyone know what the difference is between these two parts? Are
they totally interchangeable? I just want to be sure when I purchase
my new one, it's correct.

By the way, amazon.com actually has good prices on these!

Thanks!!