Primary crushers apply breakage forces by means of compression or impact. Jaw and gyratory crushers are the most common types of primary compression crushers. Each applies a compressive force to rock particles as they come in contact with the crushing surfaces. The force is applied slowly (in comparison to impact machines) resulting in abrasion and cleavage fracture. Impact crushers apply a high-speed impact force to rock particles using hammers or blow bars. The rate of energy input is much higher causing particles to shatter. Impact crushers can achieve higher reduction ratios than jaws and gyratory’s but are limited by high rates of abrasive wear and thus are restricted to somewhat softer rocks (Duthoit, 2000). In the aggregate industry, for tonnage outputs less than 1000 metric tons per hour, jaw crushers are the dominant type of primary crusher.