An impact crusher is a machine that uses striking as opposed to pressure to reduce the size of a material. Impact crushers are designated as a primary, secondary, tertiary or quarternary rotor crusher depending on which processing stage the equipment is being utilized. Common types of Impact Crushers are Horizontal Shaft Impactor (HSI) and Vertical Shaft Impactor (VSI). While the ultimate design of each type of impactor is to crush rock, their methodologies differ.