What is the black plastic disc used for that is supplied with the evofeeder automatic?

The black plastic disc helps to manually adjust the angle and the feeding amount depending on the pellet size being used on the evofeeder. It can be pushed part way into the centre hole inside the container if needed. The more you push it in, the less of a gap there is for pellets to leave from. If pushed all the way in, as a generic guideline, the amount dispersed can be reduced by 30%. Do not trap the blue wire however as this needs to spin.