A cutaway shows the bolt and clamped parts. Tightening puts the bolt in tension.
T is tightening torque and d nominal diameter. Nut factor K accounts for contact and lubrication; it is not simply friction coefficient.
Tightening torque T
20 N·m
Nut factor K (example)
0.2
Nominal thread diameter d
10 mm
Thread tensile stress area As (specified separately)
58 mm²
Orange F is axial force. Thread stress uses tensile area As, distinct from the full nominal shank area.
F · Estimated tightening preload F
10,000 N
Nominal tensile stress F/As
172.414 MPa
Blue marks inputs; orange marks outputs. These diagrams explain the fixed example below; dimensions and deformation are not drawn to physical scale.
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2. Example inputs
Tightening torque TWhat goes here?
Turning effect about an axis: force multiplied by its perpendicular moment arm.
20 N·m
Nut factor K (example)What goes here?
An empirical dimensionless nut factor in T=KFd, combining thread, bearing-surface and lubrication effects. It is not the friction coefficient μ.
The initial 0.2 is an input example. Use torque/preload tests or manufacturer values matching lubrication, coatings and reuse. A smaller K gives greater preload at the same torque; these examples do not establish allowable tightening torque.
Choose values for actual contact, lubrication, temperature and other conditions. These initial values are examples.
0.2
Nominal thread diameter dWhat goes here?
Use the dimension marked in the diagram. Distinguish radius from diameter, bore from outside diameter, and overall length from support span.
10 mm
Thread tensile stress area As (specified separately)What goes here?
Use the thread tensile stress area, not the full circular area from nominal diameter. Match the thread standard and pitch.
58 mm²
These are fixed teaching inputs. Coefficients, properties and comparison limits are not recommendations. Enter your conditions in the calculator.
3. Results for this example
Estimated tightening preload F
10,000 N
Nominal tensile stress F/As
172.414 MPa
Preload is the axial tensile force in a bolt. Nut factor K is not thread friction coefficient. Choose it for the contact and lubrication conditions.
4. Which formula is used?
T ≈ KFd, F ≈ T/(Kd), σnom = F/As
Table units are not always the units required in the formula. The calculator converts selected units to its internal base units before computing.
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Assumptions and exclusions
Nut-factor estimate. K depends on material, finish, lubrication, bearing surface and reuse; the example is not a prescribed value. Specify tensile stress area for the actual thread standard and pitch. Nominal stress does not include tightening torsion. Preload scatter, external-load sharing, loosening, bearing pressure, fatigue, thread stripping, proof strength and allowable torque are not assessed.
