A herb grinder is a tool used for breaking down cannabis. Cannabis is often sold in large pieces, and if you want to roll a blunt or pack it tightly into a bowl, you may need a herb grinder. Herb grinders allow you to break dry herbs down into smaller, more consistently-sized pieces.Herb grinders come in a small circle shape and may be made with metal, stainless steel, plastic, or wood materials. Grinders have small teeth that hold the dried herbs and break them down using a twisting motion. Herb grinders are also a must-have tool if you want to collect and add kief to your smoking experience.Cannabis grinders also come in different sizes, which affects how much cannabis you can grind each time.