Input parameters
Calculated diameters
Values are approximate and intended as a starting guide. Always confirm against tooling supplier charts and relevant standards.
Nominal pitch diameter: –
Recommended blank diameter: –
Suggested blank diameter range: –
Estimated minor diameter: –
Fundamental thread triangle height: –
| Thread system | Standard designation | Nominal major diameter | Pitch / TPI | Pitch diameter | Blank allowance factor k | Recommended blank diameter | Suggested min | Suggested max | Estimated minor diameter |
|---|---|---|---|---|---|---|---|---|---|
| Metric (example) | M6 × 1 | 6.0000 mm | 1.0000 mm | 5.3505 mm | 0.0400 | 5.3905 mm | 5.3805 mm | 5.4005 mm | 4.7731 mm |
| Metric (example) | M8 × 1.25 | 8.0000 mm | 1.2500 mm | 7.1869 mm | 0.0400 | 7.2369 mm | 7.2244 mm | 7.2494 mm | 6.4664 mm |
| Unified (example) | 7/16 - 20 UNF | 0.4375 in | 20 TPI | 0.4010 in | 0.0400 | 0.4050 in | 0.4040 in | 0.4060 in | 0.3804 in |
Formulas used in this thread rolling blank calculator
This calculator assumes a 60° symmetrical thread form, typical for metric and unified fasteners. All computations are done on the nominal profile and use a simplified model.
- Pitch (P) is the distance between corresponding points on adjacent threads along the axis. For unified threads, pitch is taken as the inverse of TPI.
-
Fundamental triangle height (H) for a 60° thread is:
H = 0.8660 × P(approximate). -
Approximate pitch diameter (D2) is estimated from the nominal major diameter (D):
D2 ≈ D − 0.6495 × P. -
Recommended blank diameter (Db) is taken slightly larger than the pitch diameter to allow
material flow during rolling:
Db ≈ D2 + k × P, where k is the blank allowance factor. -
Suggested tolerance range around the blank diameter is based on a factor t of the pitch:
Db_min = Db − t × PandDb_max = Db + t × P. -
Estimated minor (root) diameter for a 60° external thread is approximated as:
D3 ≈ D − 1.2269 × P, giving a quick indication of core section thickness.
These relationships are intended as starting values. For critical applications, always validate against current standards and your roll supplier’s recommended charts.
How to use this calculator
- Optionally choose a standard thread designation from the list. The calculator will automatically fill in the thread system, major diameter, and pitch or TPI.
- Confirm the thread system. For metric threads, you will enter pitch in millimetres; for unified threads, enter the threads per inch.
- Enter the nominal major diameter of the external thread blank. Use millimetres for metric or inches for unified threads if you are entering values manually.
- Provide the pitch or TPI. For unified threads, the calculator will convert TPI into the corresponding pitch automatically before using the formulas.
- Select a material type to pre-fill the blank allowance factor and tolerance factor. Adjust k and the tolerance factor if your process or tooling requires different values.
- Use the advanced output options to decide whether the estimated minor diameter and thread height are shown, and whether to append the result to the table.
- Click Calculate to display the pitch diameter, recommended blank diameter, suggested blank range, and optional minor diameter and triangle height.
- Use the Download CSV or Download PDF buttons to store current table data for documentation, tooling sheets, or process planning.
Role of thread rolling blanks in construction fasteners
Construction applications rely on consistent anchorage into concrete, masonry, and steel members. Correctly sized rolling blanks help ensure that critical fasteners achieve designed clamp loads and pull-out capacities without overstressing the parent material or the fastener core.
Coordinating thread blanks with slab loading checks
When designing roof pavers or pedestal systems, thread-rolled studs and anchors should be sized alongside slab loading checks. You can pair this tool with the Concrete Roof Paver Load Calculator to align fastener selection with overall panel loading.
Threaded connections in steel roof truss assemblies
Bolts and threaded rods in steel roof trusses must carry axial and shear forces reliably. Use this calculator to define suitable rolling blanks, then verify truss member forces using your structural model or the Flat Roof Truss Calculator on your construction tools hub.
Anchors and reinforcement around heavily loaded zones
Heavily loaded support points often need additional reinforcement and longer anchorage. Rolled threads allow higher fatigue performance, especially where repeated loading occurs. Combine anchor detailing with lap splice checks using the Rebar Lap Splice Length Calculator for reinforced concrete design.
Process capability and shop floor documentation
Saving thread blank calculations to CSV or PDF lets quality teams track process capability. Use exported data in your inspection plans, gauge studies, or capability indexes to prove repeatability for rolled threads used on critical construction fasteners.
Integrating thread data with other construction calculators
Thread sizes influence base plate, anchor pattern, and slab design. Combine diameter results from this page with your foundation, paver, and truss calculators to maintain a single, consistent set of fastener assumptions across your construction design workflow.
Thread rolling diameter calculator FAQs
1. Why is the thread rolling blank diameter smaller than the nominal bolt size?
The blank diameter is kept below the nominal major diameter so displaced material can flow into the die cavities. This improves crest fill, surface finish, and fatigue performance while maintaining sufficient core strength.
2. How accurate are the formulas used in this calculator?
The formulas are simplified, based on a 60° thread profile and nominal geometry. They provide realistic starting values, but you should always confirm final dimensions using current standards and data from your thread rolling die supplier.
3. Can I use these results directly for concrete anchor design?
No. The calculator only suggests appropriate rolling blanks and related diameters. Anchor pull-out resistance, edge distances, and embedment depths must be checked separately using your design code or dedicated anchor and slab loading calculators.
4. How should I choose the blank allowance factor k?
Start from the suggested range in this tool or select a material type and review the pre-filled k value. Then refine the factor after discussing with your tooling supplier and trial parts produced on your actual machines.
5. What happens if I set the tolerance factor too small?
A very small tolerance factor reduces the allowed variation in blank diameter. This can increase scrap, gauge issues, or setup time. For production environments, balance process capability with realistic machining and material variations.
6. How does this relate to roof paver and slab loading checks?
Threaded anchors in paver systems must match expected slab loading and support conditions. Use this calculator for fastener blanks and pair it with the Concrete Roof Paver Load Calculator when verifying loads on roof panels or pedestals.
7. Can I use the same settings for all construction materials?
Different materials form differently under rolling pressure, so a single allowance rarely works everywhere. Select the closest material type from the dropdown, then adjust k and tolerance after shop trials and feedback from your production and quality teams.