Works in tandem with our medium 4pc grinder olny (sold separately) Simply unscrew the storage top and replace with the top half of the four piece medium grinder and screw on. The vault will work as one unit and as you grind, herbs will fall directly into the vault. When you are done grinding, unscrew the top and replace the cap and lock. No need to transfer product from one container to the other. Grinding directly into the storage vault keeps handling herb to a minimum.