A 4-piece grinder is a type of herb grinder that consists of four interlocking pieces that work together to grind up dry herbs or other materials for smoking or vaping.

The four pieces of the grinder fit together in a top, middle, and bottom configuration, with the addition of an extra compartment above the bottom piece. The top piece typically contains the grinding teeth or pegs, while the middle piece contains holes or slots that allow the ground herbs to fall through into the bottom piece. The extra compartment in the bottom piece is designed to collect kief or pollen that falls through the screen in the middle part. One advantage of a 4-piece grinder is its ability to collect and store kief or pollen separately from the ground herbs, allowing users to save and use it later for a more potent smoking or vaping experience. The kief compartment is often removable for easy access and cleaning. Another advantage of a 4-piece grinder is that it can grind herbs more finely than a 2- or 3-piece grinder due to the additional grinding surfaces provided by the middle piece. This can result in a smoother and more consistent smoking or vaping experience.

However, 4-piece grinders are typically larger and more complex than 2- or 3-piece grinders, which can make them more difficult to use and clean. They may also be more expensive than their simpler counterparts, due to their additional features and construction.