The new valve core must match your bathtub faucet.

First, find out whether your bathtub faucet is single-handle or double-handle, single cold water faucet or hot and cold water faucet.

You also need to know the size of your bathtub faucet valve core. The valve core size refers to the water flow. Small valve cores are generally not easy to buy on the market, so you usually remove the old one and find the bathtub faucet manufacturer to replace it.