Tunnels carved from buffalo bone. These pieces are little shorter in length than our standard 12mm wearing surface. Approximate lengths are as follows: 0g: 10mm, 1g: 9mm, 2g: 9mm, 4g: 8.5mm, 6g, 8g: 8.5mm. The large pieces, 17.5mm and 7/8" are standard 12mm wearable surfaces.