Tunnels > 16 gauge ~ 1.2mm > 14 gauge ~ 1.6mm > 10 gauge ~ 2.5mm > 8 gauge - 3mm > 6 gauge ~ 4mm > 4 gauge ~ 5mm > 2 gauge ~ 6mm > 0 gauge ~ 8mm > 1/2 inch ~ 12.5mm > 7/8 inch ~ 22mm