The best way to determine what part you need to replace is to find out the brand of your faucet. Many faucet brands have lifetime warranties and will send you replacement parts for free. You can also call a customer service representative to find out which parts need to be replaced. Knowing if the faucet is hot or cold can help you determine what parts you need to replace. Also, a service representative can help you determine if you're dealing with a single or single handle bathroom faucet.