2. Tightening torque for pipe threads Proper tightening torque for pipe threads depends on combination of the materials of the male screw and female screw. In this manual, however, select tightening torque from Table 2 and Table 3 on the basis of the material of the male screw. If tightening torque is specified specially in explanation, however, apply that tightening torque. 2.1 If the male screw is made of mild steel or cast iron, apply Table 2. Table 2 Unit: Nm {kgm} 2.2 If the male screw is made of refined steel (heat-treated hard steel), apply Table 3. Table 3 Unit:
Nm {kgm} 19 Material of female thread Nominal size Steel Cast iron Light alloy 1/8 3.9 – 6.9 {0.4 – 0.7} 2.9 – 5.9 {0.3 – 0.6} 2.0 – 3.9 {0.2 – 0.4} 1/4 5.9 – 11.8 {0.6 – 1.2} 4.9 – 9.8 {0.5 – 1.0} 3.9 – 7.8 {0.4 – 0.8} 3/8 16.7 – 26.5 {1.7 – 2.7} 13.7 – 21.6 {1.4 – 2.2} 9.8 – 16.7 {1.0 – 1.7} 1/2 32.3 – 52.9 {3.3 – 5.4} 26.5 – 43.1 {2.7 – 4.4} 19.6 – 32.3 {2.0 – 3.3} 3/4 51.0 – 85.3 {5.2 – 8.7} 42.1 – 70.6 {4.3 – 7.2} 31.4 – 52.9 {3.2 – 5.4} 1 86.2 – 173.5 {8.8 – 17.7} 72.5 – 146.0 {7.4 – 14.9} 54.9 – 111.7 {5.6 – 11.4} Material of female thread Nominal size Steel Cast iron Light alloy 1/8 16.7 – 29.4 {1.7 – 3.0} 9.8 – 19.6 {1.0 – 2.0} 6.9 – 14.7 {0.7 – 1.5} 1/4 19.6 – 44.1 {2.0 – 4.5} 16.7 – 37.2 {1.7 – 3.8} 12.7 – 28.4 {1.3 – 2.9} 3/8 44.1 – 93.1 {4.5 – 9.5} 37.2 – 77.4 {3.8 – 7.9} 27.4 – 58.8 {2.8 – 6.0} 1/2 98.0 – 188.2 {10.0 – 19.2} 83.3 – 157.8 {8.5 – 16.1} 60.8 – 115.6 {6.2 – 11.8} 3/4 170.5 – 316.5 {17.4 – 32.3} 141.1 – 247.0 {14.4 – 25.2} 105.8 – 186.2 {10.8 – 19.0} 1 367.5 – 612.5 {37.5 – 62.5} 309.7 – 514.5 {31.6 – 52.5} 235.2 – 392.0 {24.0 – 40.0}