For drilling holes in small beach pebbles to use in jewelry, a 2.5mm diameter hollow coring bit works well.  The bits they sell

For drilling holes in small beach pebbles to use in jewelry, a 2.5mm diameter hollow coring bit works well.  The bits they sell that are officially for Dremels are way too expensive, I highly recommend getting your bits from Rio Grande Jewelry Supply.  They have nice packs of 5 for $14 as opposed to one official Dremel bit for more than $20!  You’ll be using all 5 of