Thread Pitch — TPI, Pitch & Standard Identification
Calculate pitch in mm or TPI, identify thread forms (UN, Metric, ACME, NPT), match unknown bolts to standards.
Why This Construction Metric Matters
Why: Thread pitch determines fastener compatibility.
How: Pitch = Length / Thread Count. TPI = 25.4 / Pitch.
- ●Measure over 1" for accuracy.
- ●Use thread gauge for unknown.
- ●Don't mix metric/imperial.
📋 Quick Examples — Click to Load
📊 Imperial Coarse vs Fine
📊 Thread Form Angles
📊 Metric Pitch by Size
📊 Your Results
Planning estimates only. Verify with a licensed engineer or contractor before construction.
📐 Construction Industry Facts
Pitch = 25.4 / TPI
— ANSI/ASME B1.1
UN/Metric 60°; ACME 29°
— ASME B1.5
Pitch (mm) = Measured Length / Thread Count. TPI = 25.4 / Pitch. 25.4 mm = 1 inch. UN/Metric 60°; ACME 29°; NPT tapered for pipe. Measure over 1" or more for accuracy.
Sources: ANSI/ASME B1.1, ISO 68-1, Machinery's Handbook.
Key Takeaways
- • Pitch = Length / Thread Count; TPI = 25.4 / Pitch (mm).
- • 1/2"-13 ≈ 1.95 mm pitch; M10×1.5 = 10mm dia, 1.5mm pitch.
- • UN/Metric 60°; ACME 29°; NPT tapered for pipe.
- • Count threads over 1" or more for unknown pitch.
Did You Know?
How Does Thread Pitch Calculation Work?
Measure Threads
Count threads over measured length. Pitch = length / count. Convert to mm if using inches.
TPI to Pitch
Pitch (mm) = 25.4 / TPI. Pitch (inches) = 1 / TPI.
Standard Match
Compare calculated pitch to UNC, UNF, Metric coarse/fine tables. Closest match identifies standard.
Expert Tips
Imperial Pitch Reference
| Diameter | Coarse | Fine |
|---|---|---|
| 1" | 10 TPI | 10 TPI |
| 1/4" | 20 TPI | 24 TPI |
| 3/8" | 16 TPI | 18 TPI |
| 1/2" | 14 TPI | 16 TPI |
| 5/8" | 12 TPI | 14 TPI |
| 3/4" | 11 TPI | 12 TPI |
Frequently Asked Questions
How do I measure thread pitch?
Count threads over a measured length; pitch = length / count. Use 1" or more for accuracy. Metric: pitch in mm. Imperial: TPI = 1/pitch (inches).
TPI to mm conversion?
Pitch (mm) = 25.4 / TPI. Example: 13 TPI → 25.4/13 ≈ 1.95 mm. 1 inch = 25.4 mm.
What is 1/2"-13?
1/2" nominal diameter, 13 threads per inch (UNC coarse). Pitch = 1/13 ≈ 0.077" ≈ 1.95 mm.
M10×1.5 meaning?
M10 = 10 mm major diameter. 1.5 = 1.5 mm pitch (distance between thread peaks). Standard metric coarse.
ACME vs UN threads?
ACME 29° for power transmission (lead screws, jacks). UN 60° for general fasteners. Different pitch systems and applications.
NPT taper pitch?
NPT is tapered; pitch varies by size. Different from UN. 1/2" NPT = 14 TPI. Used for pipe sealing.
Key Statistics
Official Data Sources
⚠️ Disclaimer: This calculator is for educational purposes only. For critical applications use certified thread gauges and professional verification.
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