If you are unfamiliar with how a grinder works we’ll touch on that here. A grinder is what you use to grind your materials into smaller pieces. The PAX grinder has been designed to grind your material down to a fine material that is great for use with vaporizers. A 3 piece grinder is a grinder that has 3 compartments – the first is the one with the teeth and where you put in your flower/herb nuggets. You then twist the lid to allow the ground up material to fall into the second compartment below. The second compartment has a screen in the bottom of it that allows very very fine crystals to fall through. The crystals fall through into the 3rd compartment and over time you can let this build up.