M39 thread: 39 × 4 mm
Threads › M39
M39 is an ISO metric coarse thread: 39 mm major diameter, 4 mm pitch, 60° form. Tap drill 35 mm. No pitch in the name means coarse pitch, 4 mm.
| Standard | ISO metric coarse |
|---|---|
| Major diameter | 39 mm |
| Pitch | 4 mm |
| Thread angle | 60° |
| Minor diameter, bolt | 34.09 mm |
| Minor diameter, nut | 34.67 mm |
| Tap drill | 35 mm |
| Usual class | 6g bolt, 6H nut |
Minor diameters worked out from the basic profile: major Ø − 1.22687 × pitch (bolt) and − 1.08253 × pitch (nut).
Open M39 in BenchsmithAdd to order list
What the call-out means
M | ISO metric |
39 | Major diameter, mm |
-6g | Bolt tolerance class (usual) |
-6H | Nut tolerance class (usual) |
Measure it
Bolt: Measure across the crests of the bolt with the caliper jaws. Worn bolts read 0.1 to 0.3 under.
Nut or tapped hole: Measure across the tops of the threads inside the nut or hole with the inside jaws. That is the minor Ø. Worn or oversize holes read a little over.
About ISO metric coarse threads
The default metric thread. If the drawing says M12 with no pitch, it's 1.75. Coarse is faster to assemble, more forgiving of dirt and damage, and won't strip as easily in soft material like aluminium or cast iron.
Measure the crests with a vernier: a worn bolt reads 0.1 to 0.3 under. Check the pitch with a gauge before you order. M12x1.75 and M12x1.5 look the same across a workshop.
Same diameter, other pitch
- M39×33 mm pitch
Close in size, won't mate
- 1-1/2-6 UNCØ38.1 mm, 6 TPI
- 1-1/2-12 UNFØ38.1 mm, 12 TPI
- 1-1/2 BSWØ38.1 mm, 6 TPI
- 1-1/2-4 ACMEØ38.1 mm, 4 TPI
- Tr40×7Ø40 mm, 7 mm pitch
One size up or down
Got a bolt and no idea what it is? Measure the outside Ø and type it into Benchsmith → Find → Thread.