Here's what I used. Be sure to buy the right size for YOUR brand and model of faucet:
Danco 80684 Faucet Repair Kit, Pack of 1, Black https://amzn.to/38cARKm
Danco 13/16 in. OD x 11/16 in. ID, Rubber, #67 O-Ring https://amzn.to/31JKo9o

How to fix a leaking Delta faucet by replacing the o-rings, seats, and springs. A very detailed step-by-step demonstration on the pieces needed to repair a leaky faucet. Tips on mistakes that can be made when trying to stop a faucet from leaking.