I've always been annoyed by the wobbly locking slider on the hopper of the Macap M2M coffee grinder. To be honest, I don't even need it, so I just dismantled the whole device. But now, the tiny coffee beans and rice grains I use for cleaning always slip out of that unsightly gap.

Here's a simple solution—its only purpose is to completely plug that loophole.
I hope this little trick can help friends in need.
Be sure to choose food-grade consumables. PLA is generally safe, but it would be even more reassuring if you could purchase certified food-grade materials.