A 4-layer metal barrel grinder is a type of herb grinder used to break down dry herbs, spices, or other plant materials into smaller, more manageable pieces. It is designed with four distinct layers, each serving a specific function in the grinding process. Here's a description of the key features and components of a 4-layer metal barrel grinder:

1. Top Lid:

   • The top layer of the grinder usually features a lid with sharp, diamond-shaped teeth or pegs on the underside.
   • Users place their herbs or spices on top of this lid before twisting the lid to grind the material.
   • The teeth effectively break down the herbs into smaller pieces when rotated against the second layer.

2. Second Layer:

   • Beneath the top lid, there's a chamber with evenly spaced holes or slots.
   • As the user grinds the material by twisting the top lid, the broken-down pieces fall through these holes and into the third layer.
   • This layer acts as a sieve, allowing only properly ground material to pass through.

3. Third Layer (Kief Chamber):

   • The third layer collects the ground material that falls through from the second layer.
   • It typically has a fine mesh screen at the bottom that allows tiny, potent particles called kief to sift through.
   • Kief is a highly concentrated form of the herb or spice and is collected at the bottom of this chamber.

4. Bottom Compartment:

   • The final layer, located at the bottom of the grinder, collects the kief that passes through the mesh screen in the third layer.
   • Users can access the kief by unscrewing the bottom compartment.
   • Kief can be collected over time and used separately or sprinkled on top of ground herbs for enhanced potency.

4-layer metal barrel grinders are favored by many users for their efficiency in grinding and for their ability to collect and preserve kief. The metal construction, often made of durable materials like aluminum or zinc alloy, ensures the grinder's longevity and resistance to wear and tear.

These grinders come in various sizes, designs, and finishes, making them popular accessories for those who enjoy using dry herbs or spices in culinary applications or for recreational purposes.