How to repair Faucet aerator?

use a washer..

Two handle, if the handle turns a full circle, it uses a washer. Either flat or beveled. If it is a quarter turn or a single handle, it uses a cup and spring. Either is easy to fix. Turn the water off. Remove the handle. There should be a cap on the top that pops off and a screw underneath. Take the screw out and remove the handle. There is a nut holding the stem down. Take that off and the full turn faucet unscrews out of the hole, the quarter turn pulls straight up. If it unscrews, the washer is on the bottom of the stem, held on with a screw. If it pull out, the cup and spring is in the bottom of the hole. Remove and replace with new. Make sure the cup is in the hole all the way around. Reassemble and the leak should be fixed. With the quarter turn faucets, there are O rings in the handle that should be changed at the same time. There should be a repair kit available for most faucet brands that has all the right pieces. $4-$6