Hoses selector gives nominal O.D. and I.D. of hoses. Use to determine ‘grip’ for connectors. Selector includes following gauges: ID’S mm 1 / 2 / 2,5 / 3 / 4 / 4,5 / 5 / 6 / 7 / 8 / 9,5 / 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 19 / 20 / 21 / 22 / 25. OD’S mm 1,5 / 2 / 2,5 / 3 / 4 / 5,5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 21.