Choose your beads according to the kind of beadwork you are going to make. You can find information about the sizes of the beads on the page Seed Bead Size.
In Bead Animals I use czech beads of sizes 9/o or 10/o. Metal wire of diameter ca. 0.30 mm fits smoothly at least twice or three times through these beads. It takes about 5-7 grams of beads to make one medium-sized bead animal.