Herb grinders, tobacco grinders or spice grinders are used to grind spices and herbs into smaller pieces to improve blending the herbs and spices together.
Using a herb grinder to shred tobacco makes your smokes smoother and your tobacco go further. They are usually cylindrical with at least 2 components that separate and have sharp teeth or pegs aligned in such a way that when both halves are turned the herb or tobacco placed inside is shredded.
Herb grinders are a must have accessory for the serious roll your own smoker.