M8×1.25 Thread Specifications
Complete dimensions for M8×1.25 coarse pitch thread per ISO 724. Pitch: 1.25mm (20.3 TPI equivalent).
Thread Dimensions
| Designation | M8×1.25 |
| Thread Series | ISO Metric Coarse |
| Pitch | 1.25 mm (20.3 TPI) |
| Major Diameter (d) | 8 mm (0.315") |
| Pitch Diameter (d₂) | 7.1881 mm (0.283") |
| Minor Diameter — External (d₁) | 6.4664 mm (0.2546") |
| Minor Diameter — Internal (D₁) | 6.6469 mm (0.2617") |
| Thread Depth | 0.6766 mm |
| Tensile Stress Area | 35.65 mm² |
| Fundamental Triangle Height (H) | 1.0825 mm |
Tap Drill Size
Recommended tap drill: 6.8 mm
Calculated minor diameter (D₁): 6.65 mm. Closest standard metric drill: 6.8 mm.
Closest inch drill: G (0.261" / 6.63 mm)
Proof Loads by Property Class
| Class | Proof Stress (MPa) | Tensile Strength (MPa) | Proof Load (kN) | Tensile Load (kN) |
|---|---|---|---|---|
| 4.6 | 225 | 400 | 8.0 | 14.3 |
| 4.8 | 310 | 420 | 11.1 | 15.0 |
| 5.8 | 380 | 520 | 13.5 | 18.5 |
| 8.8 | 580 | 800 | 20.7 | 28.5 |
| 9.8 | 650 | 900 | 23.2 | 32.1 |
| 10.9 | 830 | 1040 | 29.6 | 37.1 |
| 12.9 | 970 | 1220 | 34.6 | 43.5 |
Proof load = stress area × proof stress. Per ISO 898-1.
Related Thread Sizes
Common Applications
- General machinery
- Automotive components
- Structural brackets
- Equipment mounting
How M8×1.25 Dimensions Are Calculated
All dimensions on this page are calculated from ISO 724 formulas using the nominal diameter (8 mm) and pitch (1.25 mm):
- Fundamental triangle height: H = (√3/2) × P = 1.0825 mm
- Pitch diameter: d₂ = d − 0.6495 × P = 7.1881 mm
- Minor diameter (external): d₁ = d − 1.2269 × P = 6.4664 mm
- Minor diameter (internal): D₁ = d − 1.0825 × P = 6.6469 mm
- Thread depth: 5H/8 = 0.6766 mm
- Tensile stress area: Aₛ = (π/4) × ((d₂ + d₃)/2)² = 35.65 mm²