Size conversion table Sizes 1/8 "1/4 " 3/8 " 1/2 " 3/4 " Fit Tube OD 3.2mm 6.4mm 9.5mm 12.7mm 19.05mm BSP male thread 9.7mm 13.2mm 16.5mm 20mm 25.4mm BSP female thread 8.6mm 11.4mm 15mm 18.6mm 23.1mm