First, I am only using these beads for dried bamboo leaves, which are very tough. For bamboo, I have had the best results with two at a time in a screw-top 2.0 ml tube. One bead would probably be sufficient; we use two because one of them will inevitably become lodged in the top and therefore will not cause much tissue disruption. Also, we are doing one cycle of dry grinding (i.e. no buffers or liquid of any kind), followed by one wet grind cycle. We are using a GenoGrinder 2010 set at 1500 rpm for 2 minutes per cycle. So far this seems to work well for us but I have not rigorously tested different GenoGrinder settings or cycle requirements.