Herb Grinder with room for a magnet.
has been working for some time now without any problems!

printed at Layer height 0,15

no supports needed

there is room for a small magnet (5mmx2mm)
(you will need some glue to hold it in place)

In my experience, using a heatgun for a couple seconds on the spikes makes the layers stick together better and therefor the spikes will be stronger and wont break as easily.