Final Product and Demonstration of Function:

Notably, the red disk is mounted to a bearing through the bottom of the dispenser shell and through the shelf to keep the unit stable. Each hole in the disk is measured to be 1 teaspoon. When the hole is filled, it will stop the flow of spices from the funnel attached to the lid. 

The lid for the dispenser also features a press fit to the shell and the mentioned funnel that allows for transfer of the spices from the cavity under the iris mechanism to the iris. The bottom of the funnel sits flush with the disk to allow for stop of spice flow when obstructed.