Grinder Sponges draw water from the grinder's reservoir to the grinding head which cleans and cools the grinder head with every rotation. The sponges wets the glass edges being ground which reduces heat & friction and allows the dust that is created during grinder process to collect harmlessly in the grinder tray. Clean your sponge with clear running water prior to use, replace the sponges when worn and never use dry. Keep wet while in use. Sold in a package of 4 sponges.