Customizable bean stopper for Coffee grinder

[English]
Many of commercial coffee grinder doesn't have the stopper to prevent damaging the grinder motor. The stopper not only could prevent harming your grinder, but also can block the beans poping up from the funnel.

To make a stopper, there are 3 steps for it.

First, check your grinder funnel. Make sure the shape of the opening side is rounded, so far it doesn't support other shapes of funnel.

Second, get a vernier caliper to measure 3 value:
1. Outer diameter of opening side of