Class 1. - Light, Free-flowing , non abrasive materials such as wheat, dry rice, Beans, graphite and flour

Class 2. - Non-abrasive material that are less free-flowing than class 1 materials (small limps mixed with lines) such as baking powder, maize meal, pulverised coal, maize grits.

Class 3. - Materials similar in size and flowability to class 2 but more abrasive and requiring slower conveying speeds such as dry ashes, cement, salt, charcoal, crushed chalk.

Class 4. - Abrasive materials having poor flowability, such as coke breeze, cinders, furnace slag, cullet, crushed ore, dry sand, cement and clinker