A herb grinder is a cylindrical contraption with two halves (top and bottom) that separate and have sharp teeth or pegs aligned in such a way that when both halves are turned, material inside—typically tobacco

Tobacco

Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...

 or marijuana—is shredded, resulting in a product that burns more evenly.

Herb grinders can be used to make tobacco snuff. Snuff

Snuff

Snuff is a product made from ground or pulverised tobacco leaves. It is an example of smokeless tobacco. It originated in the Americas and was in common use in Europe by the 17th century...

 is produced when tobacco is ground into a fine powder, so it can be consumed without smoking.

Some grinders

Mill (grinding)

A grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many different types of grinding mills and many types of materials processed in them. Historically mills were powered by hand , working animal , wind or water...

 also have two or three compartments instead of just one, with a fine screen

Sieve

A sieve, or sifter, separates wanted elements from unwanted material using a woven screen such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid...

 separating the bottom compartment from the top. This allows fine particles such as pollen

Pollen

Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

 to pass through, but blocks larger plant material.

Grinders called "four-stages" are also popular. "Four-stages" are similar to regular grinders, but include a second fine screen to further separate pollen

Pollen

Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

or other tiny plant matter.

Herb grinders are also used to prepare spices and cooking herbs for culinary preparation.