Skin Eyelets > Tunnels > 10 gauge ~ 2.5mm > 6 gauge ~ 4mm > 4 gauge ~ 5mm > 2 gauge ~ 6mm > 0 gauge ~ 8mm > 00 gauge ~ 9.5mm > 1/2 inch ~ 12.5mm > 1-1/2 inch ~ 38mm > 1-5/8 inch ~ 41mm