A carbon brush is a component used to conduct electrical current between the stationary and rotating parts of a motor. In a generator or motor, the commutator rotates on a shaft and the fixed carbon brush rides on it to permit the flow of electricity and complete a circuit. Carbon brushes are available in four main grade categories: carbon graphite, electrographitic, graphite, and metal graphite.Metal graphite carbon brushes for electrical motors are often made from natural graphite and fine metal powders. Copper is the most common, but silver, tin and lead are sometimes used. Metal graphite brushes are ideal for many applications due to low resistivity. Metal graphite brushes are used on commutators of plating generators that have low voltage and high brush current densities. They operate on rings of wound rotor induction motors where high brush current densities are also found. Metal graphite brushes are used with grounding brushes because of their low contact drop.