M39 Thread Specs
Standard: ISO 261 (ISO Metric Coarse)
This reference guide outlines the technical dimensions and tapping parameters for the standard M39 metric thread.
Part of the ISO Metric Coarse series defined by ISO 261, the thread features a nominal diameter of 39 mm and a pitch of 4 mm.
For machining or fabrication, the recommended tap drill size is 35 mm (for 75% thread depth) or 35.25 mm (for 65% thread depth).
Dimensional Specifications (mm)
Nominal Diameter
39 mm
Pitch
4 mm
Threads per mm
0.25
Major Diameter
39 mm
Pitch Diameter (d₂)
36.402 mm
Minor Diameter (d₁) Ext
34.67 mm
Minor Diameter (D₁) Int
35.247 mm
Thread Height
3.464 mm
Root Radius
0.577 mm
Drilling & Strength Specs
Tap Drill (75%)
35 mm
Tap Drill (65%)
35.25 mm
Stress Area
975.75 mm²
Stress Diameter
34.093 mm
Recommended Tightening Torque
| Property Class | Dry (Nm) | Lubricated (Nm) |
|---|---|---|
| Class 8.8 | 4080 | 3060 |
| Class 10.9 | 5997 | 4497.8 |
| Class 12.9 | 7196 | 5397 |
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Frequently Asked Questions
What is the tap drill size for a M39 thread?
For standard thread engagement (approx. 75%), the recommended tap drill size for M39 is 35 mm. For a slightly looser 65% thread engagement, a 35.25 mm drill bit is recommended.
What is the pitch of a M39 thread?
The thread pitch for a standard M39 thread is 4 mm, which equates to approximately 0.25 threads per millimeter.
What are the major and pitch diameters for M39?
The nominal major diameter of M39 is 39 mm. The calculated pitch diameter (d₂) is 36.402 mm per the ISO 68-1/ISO 261 standards.