Use this thread stripping calculator to estimate the internal and external thread shear capacity of a bolted joint. The calculator compares the applied tensile load with the approximate thread stripping capacity based on thread diameter, pitch, engagement length and allowable shear stress.
This calculator estimates whether the internal or external thread is likely to strip under axial tensile load. It calculates approximate internal thread shear area, external thread shear area, thread stripping capacity, utilisation, factor of safety and the governing failure mode.
The calculator provides:
This calculator is useful for tapped holes, nuts, threaded inserts and preliminary checks where thread stripping may control the bolted joint strength.
Approximate mean thread diameter:
Approximate internal thread shear area:
Approximate external thread shear area:
Internal thread stripping capacity:
External thread stripping capacity:
Design allowable shear stresses:
Governing stripping capacity:
Utilisation:
Factor of safety:
| Symbol | Description | Units |
|---|---|---|
| F | Applied axial tensile load | N |
| d | Nominal thread diameter | mm |
| p | Thread pitch | mm |
| dm | Approximate mean thread diameter | mm |
| Le | Thread engagement length | mm |
| Asi | Approximate internal thread shear area | mm² |
| Ase | Approximate external thread shear area | mm² |
| τi,allow | Allowable internal thread shear stress | N/mm² |
| τe,allow | Allowable external thread shear stress | N/mm² |
| SF | Safety factor | - |
| Joint Type | Likely Governing Check |
|---|---|
| Steel bolt into steel nut | Bolt tensile stress or thread stripping may govern depending on engagement length. |
| Steel bolt into aluminium tapped hole | Internal thread stripping in the softer material may govern. |
| Short nut or shallow tapped hole | Thread engagement length may be insufficient. |
| Threaded insert | Both internal and external thread interfaces may need checking separately. |
Enter the thread details and applied load, then click calculate.
| Result | Meaning |
|---|---|
| Internal thread capacity | The approximate stripping capacity of the nut or tapped hole thread. |
| External thread capacity | The approximate stripping capacity of the bolt or screw thread. |
| Governing capacity | The lower of the internal and external thread stripping capacities. |
| Governing mode | The thread interface with the lower calculated stripping capacity. |
| Utilisation | The applied tensile load divided by the governing thread stripping capacity. A value below 100% passes this simplified check. |
| Factor of safety | The governing stripping capacity divided by the applied tensile load. |
This calculator provides a simplified internal and external thread stripping check. It should not be used as the only basis for final fastener design.
| This Calculator Includes | This Calculator Does Not Include |
|---|---|
| Approximate internal thread shear capacity | Detailed ISO, ASME or fastener standard thread stripping equations |
| Approximate external thread shear capacity | Thread tolerance class effects |
| Governing thread stripping mode | Unequal load distribution between engaged threads |
| Utilisation and factor of safety | Material hardness, galling, coatings or lubrication effects |
| Worked calculation | Fatigue, preload relaxation, prying action or joint stiffness |
For estimating required engagement length, use the Thread Engagement Length Calculator.
For calculating thread tensile stress area, use the Thread Tensile Stress Area Calculator.
For checking bolt tensile stress, use the Bolt Tensile Stress Calculator.
Thread stripping occurs when the engaged internal or external threads shear off before the bolt or joint reaches the desired load capacity. This is especially important for tapped holes in softer materials, short nuts and threaded inserts.
This calculator uses an approximate cylindrical shear area based on the mean thread diameter and engagement length. The same geometric area is used for the internal and external thread interface, while different allowable shear stresses may be entered for the two materials.
The weaker material usually controls the stripping capacity. For example, a steel bolt in an aluminium tapped hole is often governed by the internal aluminium thread capacity rather than the steel bolt thread.
For further screw thread data, see the RoyMech reference pages: Screw Stress Areas and ISO Metric Thread Dimensions.
For the full calculator section, see: Bolted Joint Calculators.
Thread stripping is a failure mode where the engaged internal or external threads shear off under load. It can occur before bolt tensile failure if the engagement length or thread material strength is insufficient.
The weaker material usually strips first. For example, a steel bolt screwed into an aluminium tapped hole may strip the internal aluminium thread before the steel bolt thread fails.
A simplified method estimates thread stripping capacity from thread shear area and allowable shear stress:
No. Thread stripping is a shear failure of the engaged threads. Bolt tensile failure is a tensile failure through the bolt cross-section.
Thread stripping capacity can be increased by increasing engagement length, using a stronger tapped material, using an insert, using a larger thread diameter or reducing the applied load.
This calculator is intended for preliminary engineering calculations and educational use. Final design should use the relevant thread standard, material data, thread tolerance, engagement length rules and safety factors.