Thread Specs — UNC, UNF & Metric ISO
Calculate major, minor, pitch diameter, tensile area. Class 2A commercial; 3A precision. 60° thread form.
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📊 Thread Dimensions
📊 Class Tolerance
📊 UNC TPI by Size
📊 Pitch by Series
Planning estimates only. Verify with a licensed engineer or contractor before construction.
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Minor = Major − 1.082532 × Pitch
— ASME B1.1
Pitch diameter = Major − 0.649519 × Pitch
— ISO 261
Thread dimensions: Minor = Major − 1.082532×Pitch; Pitch Dia = Major − 0.649519×Pitch (60° UN/Metric). Tensile area = π/4×(Pitch Dia)². Class 2A commercial; 3A precision. Pitch (in) = 1/TPI.
Sources: ASME B1.1, ISO 261, Machinery's Handbook.
Key Takeaways
- • Minor = Major − 1.082532×Pitch; Pitch Dia = Major − 0.649519×Pitch.
- • 1/4-20 UNC: Major 0.25", Pitch 0.05"; M10×1.5: 10mm, 1.5mm pitch.
- • Class 2A = commercial; 3A = precision. A = external, B = internal.
- • Tensile Area = π/4 × (Pitch Dia)² for strength.
Did You Know?
How Does Thread Calculation Work?
Minor Diameter
Minor = Major − 1.082532×Pitch for 60° threads. Defines root of thread.
Pitch Diameter
Pitch Dia = Major − 0.649519×Pitch. Effective diameter for fit and strength.
Tensile Area
Area = π/4 × (Pitch Dia)². Used for bolt load capacity.
Expert Tips
Thread Class Comparison
| Class | Description | Tolerance |
|---|---|---|
| 1A/1B | Loose fit | ±3 mils |
| 2A/2B | Standard commercial | ±2 mils |
| 3A/3B | Precision | ±1 mil |
Frequently Asked Questions
What is pitch diameter?
Pitch diameter is the effective diameter where thread thickness equals the space between threads. Used for fit and strength. Formula: Pitch Dia = Major − 0.649519 × Pitch (60° UN/Metric).
UNC vs UNF threads?
UNC (coarse) has fewer threads per inch, stronger in soft materials. UNF (fine) has more TPI, better in hard materials. 1/4-20 UNC: 20 TPI; 1/4-28 UNF: 28 TPI.
Class 2A vs 3A thread tolerance?
Class 2A/2B = commercial, most common. Class 3A/3B = precision, tighter tolerance. A = external (bolt), B = internal (nut). Match 2A with 2B, 3A with 3B.
How to convert TPI to pitch?
Pitch (inches) = 1 / TPI. Example: 20 TPI → pitch = 0.05". Metric pitch is in mm directly (e.g., M10×1.5 = 1.5 mm pitch).
What is tensile stress area?
Tensile area = π/4 × (Pitch Diameter)². Used for bolt strength calculations. Smaller than nominal cross-section due to thread roots.
M10×1.5 meaning?
M10 = 10 mm major diameter. 1.5 = 1.5 mm pitch (distance between thread peaks). Standard metric coarse thread.
Key Statistics
Official Data Sources
⚠️ Disclaimer: This calculator is for educational purposes only. Critical applications require certified gauging and professional verification.
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