Kibble should be no larger than .75 inches in length/diameter. If your pet requires disc-type (prescription) kibble you can rest assured that our feeder is designed to dispense these without jamming. It is important to test the portion of meal dispensed and to ensure that kibble flows freely, before programming the feeder for operation. For the test, power the feeder on and move the manual “Cup Size Adjuster” which is located on the inner wall of the main (black) hopper one notch above the lowest position. This position usually allows the free flow of average size kibble without obstruction. Next, press and hold the FORWARD button for approximately 5 seconds, releasing the button when the impeller rotates. Based on the portion dispensed, the “Cup Size Adjuster” can be adjusted (upwards) incrementally, to attain the desired amount.