The document discusses four types of apron feeders: 1) GBH New Type Medium Size Apron Feeder, 2) GBH Type Medium Size Apron Feeder, 3) GBZ Type Heavy Duty Apron Feeder, and 4) New Type Medium Size Apron Feeder. All four types are used to transport materials of different sizes and densities in industries like building materials, chemicals, metallurgy, and coal. They operate using chains to pull materials along an inclined trough and can be adjusted for optimal efficiency when interfacing with receiving devices.