The Rancilio Rocky is a popular coffee grinder with one major annoyance: beans and ground coffee get caught in the deep screw wells of the hopper. Beans are easily tapped back into the burrs, but the grounds remain and eventually turn rancid. These flavors find their way back into fresh grounds and on to your cup, contributing disappointment and truck-stop to the flavor profile.

This is essentially a form-fitting Rocky bean funnel. It sits snugly in the hopper, with the body covering the wells and the slight throat preventing grounds from kicking back up from underneath the insert.

Other bright minds are hard at work on this problem. Here's another design that fills each screw well with an individual plug:
http://www.thingiverse.com/thing:621599

-NOS