This is a conveyor bed. A pulley is like an IRON pipe. Pulleys are put on each end of the bed. Each pulley has a steel shaft through it. The shaft turns on a bearing . . .
Bearings use little steel balls to keep the pulley shaft and the conveyor bed from rubbing together.
Now the shaft can turn easily. The drive pulley is usually larger because it does the work. A sprocket is put on the drive pulley shaft. A sprocket is put on the motor. The chain moves when the motor is started.