The design of a Screw feeder resembles to that of a Screw Conveyor closely but unlike a screw conveyor, a screw feeder is required to be very precise and accurate. While in a Screw conveyor the screw is filled to the extent of 30% to 40%, in a screw feeder the material completely fills the screw. This is the reason why the material is discharged with uniform and controlled rate and the rate can be varied by controlling the speed of rotation of the screw.