M8 Thread Specs
Standard: ISO 261 (ISO Metric Coarse)
This reference guide outlines the technical dimensions and tapping parameters for the standard M8 metric thread.
Part of the ISO Metric Coarse series defined by ISO 261, the thread features a nominal diameter of 8 mm and a pitch of 1.25 mm.
For machining or fabrication, the recommended tap drill size is 6.75 mm (for 75% thread depth) or 6.83 mm (for 65% thread depth).
Dimensional Specifications (mm)
Nominal Diameter
8 mm
Pitch
1.25 mm
Threads per mm
0.8
Major Diameter
8 mm
Pitch Diameter (d₂)
7.188 mm
Minor Diameter (d₁) Ext
6.647 mm
Minor Diameter (D₁) Int
6.827 mm
Thread Height
1.083 mm
Root Radius
0.18 mm
Drilling & Strength Specs
Tap Drill (75%)
6.75 mm
Tap Drill (65%)
6.83 mm
Stress Area
36.61 mm²
Stress Diameter
6.466 mm
Recommended Tightening Torque
| Property Class | Dry (Nm) | Lubricated (Nm) |
|---|---|---|
| Class 8.8 | 31 | 23.3 |
| Class 10.9 | 46 | 34.5 |
| Class 12.9 | 55 | 41.3 |
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Frequently Asked Questions
What is the tap drill size for a M8 thread?
For standard thread engagement (approx. 75%), the recommended tap drill size for M8 is 6.75 mm. For a slightly looser 65% thread engagement, a 6.83 mm drill bit is recommended.
What is the pitch of a M8 thread?
The thread pitch for a standard M8 thread is 1.25 mm, which equates to approximately 0.8 threads per millimeter.
What are the major and pitch diameters for M8?
The nominal major diameter of M8 is 8 mm. The calculated pitch diameter (d₂) is 7.188 mm per the ISO 68-1/ISO 261 standards.