The flippers who installed the plastic shower liner only cut the faucet handle holes big enough for the stems and I need to replace the cartridges. I used a jab saw for one but that sucked, what kind of Dremel bit can I use?
Roto-zip might be you answer
Roto-zip could work well like the other poster said. If you don’t have access to one, you can also use the abrasive sanding bits for the dremel, you may chew through a couple, but they work in a pinch.
Go get a diamond hole bit and use a coke bottle full of water with a hole poked in the top to cool and lube it. Use a drill instead of a dremel. You will likely chip the fiberglass (I’m assuming that’s what you think is plastic) if you try with a rotozip bit.
Alas, this won’t work because the stem is in the way. Thanks for the recommendation, though!