Thread inputs
How to use this calculator
Select a thread standard and thread type first. Enter pitch or threads per inch next. Then provide the diameter needed for your chosen mode.
Add tolerance, allowance, and machining details when available. Choose custom geometry for uncommon thread profiles. Review warnings before using any production dimensions.
Radial depth measures one side of the thread. Diametral depth equals twice the radial depth. Always confirm final dimensions with the governing engineering standard.
Thread depth reference table
| Profile | Included angle | Approximate radial depth | Important note |
|---|---|---|---|
| ISO Metric external | 60° | 0.61343 × pitch | Basic-profile approximation |
| ISO Metric internal | 60° | 0.54127 × pitch | Basic-profile approximation |
| Unified external | 60° | 0.61343 × pitch | Allowance changes limits |
| Whitworth and BSP | 55° | 0.640327 × pitch | Rounded crest and root |
| NPT and NPTF | 60° | 0.80000 × pitch | Taper and gauge planes matter |
| ACME | 29° | 0.50000 × pitch | Add clearance when required |
| Metric trapezoidal | 30° | 0.50000 × pitch | Verify standard clearances |
Example data
| Designation | Pitch | External radial depth | Approximate minor diameter |
|---|---|---|---|
| M6 × 1 | 1.0000 mm | 0.6134 mm | 4.7731 mm |
| M10 × 1.5 | 1.5000 mm | 0.9201 mm | 8.1597 mm |
| 1/4-20 UNC | 0.0500 in | 0.0307 in | 0.1887 in |
| 1/2-10 ACME | 0.1000 in | 0.0500 in | 0.4000 in |
Pitch, lead, and thread depth
Pitch is the spacing between corresponding adjacent thread points. Lead is axial travel during one complete revolution. Single-start threads have equal pitch and lead.
Multi-start threads multiply pitch by their start count. Greater lead also increases the calculated helix angle. Thread depth remains based primarily on profile geometry.
Internal and external basic depths can differ by standard. Tolerances further change acceptable manufactured diameter limits. Gauges remain essential for reliable production thread inspection.
Machining guidance
Use lighter cuts as the tool approaches final depth. Spring passes can reduce deflection-related dimensional variation. Cutting conditions still depend heavily on material.
Tool-tip radius changes the effective generated thread profile. Flank infeed can reduce cutting load substantially. CNC cycles may distribute cuts differently by controller.
Measure pitch diameter whenever fit is especially important. Use wires, gauges, or calibrated thread measuring equipment. Never rely only on calculated radial tool movement.
Frequently asked questions
What is radial thread depth?
Radial depth measures crest-to-root distance on one side. It describes actual inward or outward tool travel. Diametral depth is always twice this calculated amount.
Why do internal and external depths differ?
Many standards truncate internal and external profiles differently. These truncations create clearance and practical manufacturing limits. Therefore their basic radial depths may differ slightly.
Can this calculator replace standard tables?
No calculator replaces authoritative dimensional tables or gauges. Thread standards contain allowances, deviations, radii, and exceptions. Verify every production dimension against its governing specification.
How are pitch and TPI converted?
Metric pitch converts using twenty-five point four millimeters. Divide 25.4 by pitch to obtain TPI. Divide 25.4 by TPI for millimeter pitch.
What does multi-start lead mean?
Lead equals pitch multiplied by the thread starts. Two starts produce twice the single pitch travel. More starts also increase helix angle significantly.
How does taper affect pipe threads?
Taper changes diameter continuously along the threaded length. Pipe standards define specific gauge planes and engagement. Use official dimensions for sealing thread acceptance.
What is the full-profile height?
It is the untruncated theoretical thread triangle height. Real threads remove material from crests and roots. Practical depth is consequently smaller than full height.
Why add stock allowance?
Allowance reserves material for finishing or fit adjustment. Positive allowance increases the suggested final cutting depth. Use values approved by the machining plan.
Does tool-tip radius affect depth?
Yes, radius changes crest and root generation geometry. The calculator provides a simplified compensation estimate only. Confirm tool geometry using its manufacturer specifications.
How many threading passes should I use?
Pass count depends on pitch, material, rigidity, and tooling. Coarse threads usually require more progressively lighter passes. Follow machine and tooling recommendations for safety.
Why should pitch diameter be measured?
Pitch diameter strongly controls mating fit and interchangeability. Major and minor diameters alone cannot prove fit. Proper gauges provide the most reliable verification.
Limitations and safety notice
This tool provides educational geometry and machining estimates. Standards include details beyond simplified calculator coefficients. Results should not replace certified engineering documentation.
Machine tools can cause severe injury during operation. Follow guarding, workholding, tooling, and inspection procedures. Stop immediately whenever cutting behavior becomes unsafe.
Pressure-containing and safety-critical threads require additional verification. Use qualified personnel and calibrated inspection equipment. Final responsibility remains with the designer and manufacturer.