M18 A2-70 tightening torque — 218.3 N·m
192.47 mm² of thread at 450 MPa yield gives a target clamp force of 60628 N. The torque here is what it takes to produce that stretch.
Tightening torque
Roughly half the effort is lost to friction in the threads and another half under the head. Only about a tenth actually stretches the bolt. Oil the thread and the same clamp force needs a quarter less torque — and applying a dry-spec torque to an oiled bolt overtightens it by that same quarter.
- zinc-plated, as it comesK=0.22240.1 N·m
- plain dry steelK=0.2218.3 N·m
- lightly oiledK=0.15163.7 N·m
- waxed or moly-coatedK=0.12131 N·m
- Strength grade
- A2-70
- Pitch
- 2.5 mm
- Cross-section
- 192.47 mm²
- Tensile strength
- 700 MPa
- Yield strength
- 450 MPa
- Target clamp force
- 60628 N
- Force that breaks it
- 134729 N
- In kgf·m
- 22.26 kgf·m
- In lb-ft
- 161 lb-ft
These figures are a starting point
Whenever the manufacturer specifies a torque, that number wins. Bolts into aluminium, bolts squeezing a gasket and bolts with thread locker are all set differently from this calculation.
Nearby cells
Same bolt, other grades
Same grade, other bolts
How to read this
- Torque turns the bolt; what you want is the clamp force the stretched bolt provides.
- The slipperier the thread, the less torque the same clamp force needs — pick the condition you have.
- Clamp force is set at 70% of yield. A manufacturer figure always wins over this one.
- These are coarse threads. A fine thread has slightly more area, so its numbers differ.
Frequently asked questions
Q. What torque does a M18 A2-70 bolt take?
218.3 N·m dry — 22.26 kgf·m, or 161 lb-ft.
Q. And if the thread is oiled?
163.7 N·m. Lower friction means lower torque for the same clamp force.
Q. How hard does this bolt actually bite?
The target clamp force is 60628 N. It breaks at 134729 N, so you stop at 45% of that.
Q. How strong is grade A2-70?
700 MPa tensile, 450 MPa yield. Multiply by the 192.47 mm² of thread and you have what this bolt can hold.