Just ordered 20 - thanks for the tip!I got the 3" ones off of Amazon, https://www.amazon.com/gp/product/B00OWKP1TY/ref=pe_1843280_285037640_em_1p_0_ti?pldnSite=1
They are thin, if you drop them on the ground they will likely break. Of the 20, only 1 came broken in 2. They are wrapped really well, but super glue will fix anything broken. If you are trying to grow something out on them, they would be really be awesome for cutting up. Sitting on the bottom of my tank, I think they will do well.