Three-piece grinders do not collect kief. If you are interested in a dry herb grinder that does collect kief, you will want to invest in a four-piece grinder, as the fourth piece is indicative of a screen that allows kief to pass through and collect in a container below. Collecting kief is a great way to get the most out of the dry herbs you grind, so make sure you purchase a four-piece grinder if you are wanting to enjoy the kief that is produced from grinding!