M18×2.5 Thread Specifications
Complete dimensions for M18×2.5 coarse pitch thread per ISO 724. Pitch: 2.5mm (10.2 TPI equivalent).
Thread Dimensions
| Designation | M18×2.5 |
| Thread Series | ISO Metric Coarse |
| Pitch | 2.5 mm (10.2 TPI) |
| Major Diameter (d) | 18 mm (0.7087") |
| Pitch Diameter (d₂) | 16.3762 mm (0.6447") |
| Minor Diameter — External (d₁) | 14.9327 mm (0.5879") |
| Minor Diameter — Internal (D₁) | 15.2937 mm (0.6021") |
| Thread Depth | 1.3532 mm |
| Tensile Stress Area | 192.47 mm² |
| Fundamental Triangle Height (H) | 2.1651 mm |
Tap Drill Size
Recommended tap drill: 15.5 mm
Calculated minor diameter (D₁): 15.29 mm. Closest standard metric drill: 15.5 mm.
Closest inch drill: 39/64" (0.6094" / 15.48 mm)
Proof Loads by Property Class
| Class | Proof Stress (MPa) | Tensile Strength (MPa) | Proof Load (kN) | Tensile Load (kN) |
|---|---|---|---|---|
| 4.6 | 225 | 400 | 43.3 | 77.0 |
| 4.8 | 310 | 420 | 59.7 | 80.8 |
| 5.8 | 380 | 520 | 73.1 | 100.1 |
| 8.8 | 580 | 800 | 111.6 | 154.0 |
| 9.8 | 650 | 900 | 125.1 | 173.2 |
| 10.9 | 830 | 1040 | 159.8 | 200.2 |
| 12.9 | 970 | 1220 | 186.7 | 234.8 |
Proof load = stress area × proof stress. Per ISO 898-1.
Related Thread Sizes
Common Applications
- Structural connections
- Heavy equipment
- Pressure vessels
- Large flanges
How M18×2.5 Dimensions Are Calculated
All dimensions on this page are calculated from ISO 724 formulas using the nominal diameter (18 mm) and pitch (2.5 mm):
- Fundamental triangle height: H = (√3/2) × P = 2.1651 mm
- Pitch diameter: d₂ = d − 0.6495 × P = 16.3762 mm
- Minor diameter (external): d₁ = d − 1.2269 × P = 14.9327 mm
- Minor diameter (internal): D₁ = d − 1.0825 × P = 15.2937 mm
- Thread depth: 5H/8 = 1.3532 mm
- Tensile stress area: Aₛ = (π/4) × ((d₂ + d₃)/2)² = 192.47 mm²