Grinders are tools used to quickly break herb up for wrapping in papers, filling vaporizers or packing into a hand pipe. Grinding herb greatly increases surface area and airflow and results in smoother hits. Grinders come in many shapes and sizes. They can be simple, two-piece plastic units, or multi-layered machines made of precious metals. Grinders can come in many shapes and sizes, with different ergonomic designs, different finishes, different colors and even differently shaped teeth. One common feature on a grinder is a kief catcher. Kief catchers store trichromes that fall through a pollen screen under one chamber of the grinder. When enough kief is collected, it can be pressed into hash, cooked with or sprinkled on a bowl for some extra oomph. Kief catchers can keep a grinder clean and maximize your money by giving your herb a little extra life. Another common feature is a magnetic hinge. Magnetic hinges allow the grinder to be turned smoothly, but also remain closed to prevent the ground herb from getting stale.