Torque values metric fasteners
Control of tightening torque in metric threaded joints is essential to ensure proper preload without exceeding the yield strength of the bolt. The values in this guide are based on coarse ISO metric threads, with slightly lubricated threads and an assembly stress equivalent to 85 % of the proof load. Data is presented for the most commonly used property classes in engineering — 8.8, 9.8, 10.9 and 12.9 — according to ISO 898‑1 and the withdrawn ASTM F568M.
Coarse ISO Metric Thread Dimensions
Section titled “Coarse ISO Metric Thread Dimensions”| Metric designation | Nominal diameter (mm / in) | Pitch (mm / in) | Recommended tap drill (mm / in) |
|---|---|---|---|
| M5 × 0,8 | 5 mm / 0,197 in | 0,8 mm / 0,0315 in | 4,2 mm / 0,165 in |
| M6 × 1,0 | 6 mm / 0,236 in | 1,0 mm / 0,0394 in | 5,0 mm / 0,197 in |
| M8 × 1,25 | 8 mm / 0,315 in | 1,25 mm / 0,0492 in | 6,8 mm / 0,268 in |
| M10 × 1,5 | 10 mm / 0,394 in | 1,5 mm / 0,0591 in | 8,5 mm / 0,335 in |
| M12 × 1,75 | 12 mm / 0,472 in | 1,75 mm / 0,0689 in | 10,2 mm / 0,402 in |
| M16 × 2,0 | 16 mm / 0,630 in | 2,0 mm / 0,0787 in | 14,0 mm / 0,551 in |
| M20 × 2,5 | 20 mm / 0,787 in | 2,5 mm / 0,0984 in | 17,5 mm / 0,689 in |
| M24 × 3,0 | 24 mm / 0,945 in | 3,0 mm / 0,1181 in | 21,0 mm / 0,827 in |
| M30 × 3,5 | 30 mm / 1,181 in | 3,5 mm / 0,1378 in | 26,5 mm / 1,043 in |
Allowable Loads According to Property Class
Section titled “Allowable Loads According to Property Class”| Class | Diameter range | Proof load (MPa / ksi) | Yield strength (MPa / ksi) | Tensile strength (MPa / ksi) |
|---|---|---|---|---|
| 8.8 | ≤ 16 mm | 580 MPa / 84,1 ksi | 640 MPa / 92,8 ksi | 800 MPa / 116,0 ksi |
| 8.8 | 17‑72 mm | 600 MPa / 87,0 ksi | 660 MPa / 95,7 ksi | 830 MPa / 120,4 ksi |
| 10.9 | all diameters | 830 MPa / 120,4 ksi | 940 MPa / 136,3 ksi | 1 040 MPa / 150,8 ksi |
| 12.9 | all diameters | 970 MPa / 140,7 ksi | 1 100 MPa / 159,5 ksi | 1 220 MPa / 176,9 ksi |
Recommended Tightening Torques
Section titled “Recommended Tightening Torques”The torques indicated correspond to coarse thread, slightly lubricated threads and preload equivalent to 85 % of the proof load. Values in Nm and lb‑ft.
| Size (mm) | Class 8.8 (Nm / lb‑ft) | Class 9.8 (Nm / lb‑ft) | Class 10.9 (Nm / lb‑ft) | Class 12.9 (Nm / lb‑ft) |
|---|---|---|---|---|
| M5 | 7,0 Nm / 5,2 lb‑ft | 7,8 Nm / 5,8 lb‑ft | 10,0 Nm / 7,4 lb‑ft | 11,7 Nm / 8,6 lb‑ft |
| M6 | 11,8 Nm / 8,7 lb‑ft | 13,3 Nm / 9,8 lb‑ft | 17,0 Nm / 12,5 lb‑ft | 19,9 Nm / 14,7 lb‑ft |
| M8 | 28,8 Nm / 21,2 lb‑ft | 32,3 Nm / 23,8 lb‑ft | 41,3 Nm / 30,5 lb‑ft | 48,3 Nm / 35,6 lb‑ft |
| M10 | 57,3 Nm / 42,3 lb‑ft | 64,1 Nm / 47,3 lb‑ft | 81,8 Nm / 60,3 lb‑ft | 95,7 Nm / 70,6 lb‑ft |
| M12 | 99,8 Nm / 73,6 lb‑ft | 112 Nm / 82,6 lb‑ft | 143 Nm / 105,5 lb‑ft | 167 Nm / 123,2 lb‑ft |
| M16 | 248 Nm / 182,9 lb‑ft | 277 Nm / 204,3 lb‑ft | 354 Nm / 261,1 lb‑ft | 413 Nm / 304,6 lb‑ft |
| M20 | 500 Nm / 368,8 lb‑ft | — | 690 Nm / 508,9 lb‑ft | 809 Nm / 596,7 lb‑ft |
| M24 | 865 Nm / 638,0 lb‑ft | — | 1 195 Nm / 881,4 lb‑ft | 1 395 Nm / 1 028,9 lb‑ft |
| M30 | 1 719 Nm / 1 267,9 lb‑ft | — | 2 377 Nm / 1 753,2 lb‑ft | 2 774 Nm / 2 046,0 lb‑ft |
Standards Equivalencies
Section titled “Standards Equivalencies”| Property class | Current ISO standard | Corresponding DIN standard | Historical ASTM standard |
|---|---|---|---|
| 8.8 | ISO 898‑1:2013 | DIN EN ISO 898‑1 | ASTM F568M Class 8.8 (withdrawn) |
| 10.9 | ISO 898‑1:2013 | DIN EN ISO 898‑1 | ASTM F568M Class 10.9 (withdrawn) |
| 12.9 | ISO 898‑1:2013 | DIN EN ISO 898‑1 | ASTM F568M Class 12.9 (withdrawn) |
Factors Affecting Tightening Torque
Section titled “Factors Affecting Tightening Torque”A 30% increase in torque is necessary when bolts are tightened dry, compared to the value for lightly lubricated threads. Conversely, generous lubrication can reduce the required torque by up to 40%. The tables in this document assume light oil lubrication.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum torque for an M8 class 8.8 bolt?
Section titled “What is the maximum torque for an M8 class 8.8 bolt?”28,8 Nm (21,2 lb‑ft) when the thread is lightly lubricated and the preload is limited to 85 % of the proof load.
What tightening torque should be applied to an M12 class 10.9 bolt?
Section titled “What tightening torque should be applied to an M12 class 10.9 bolt?”143 Nm (105,5 lb‑ft) for coarse metric thread with light lubrication, according to the recommended torque table.
Is a 30% increase in torque sufficient to compensate for lack of lubrication?
Section titled “Is a 30% increase in torque sufficient to compensate for lack of lubrication?”Yes, when threads are assembled completely dry, approximately 30% more torque is required to achieve the same preload as with light lubrication, although it is recommended to verify by testing.
What is the minimum tensile strength of a class 12.9 bolt?
Section titled “What is the minimum tensile strength of a class 12.9 bolt?”1 220 MPa (176,9 ksi) for all diameters, according to ISO 898‑1.
What drill bit is needed for an M10 × 1,5 threaded hole?
Section titled “What drill bit is needed for an M10 × 1,5 threaded hole?”An 8,5 mm (0,335 in) diameter drill bit is required.
Are metric class 8.8 bolts according to ASTM F568M and ISO 898‑1 equivalent?
Section titled “Are metric class 8.8 bolts according to ASTM F568M and ISO 898‑1 equivalent?”Yes, the mechanical properties of class 8.8 defined in the old ASTM F568M coincide with those of ISO 898‑1; both standards are interchangeable at the design level.