Otherwise you will have a gap like this. now you are done with the replacement of the cartridge. but don't put the handle back on yet. use the handle to turn the faucet off, then turn the water to the house back on. make sure to turn both the hot and cold back on if you turned them both off. You may need to adjust the scald guard feature of the new faucet. with the handle on temporarily turn the faucet on as far to the hot side as it will go.