M2 Tap Drill Size (M2 x 0.4)
ISO metric coarse · 0.4 mm pitch · ISO 261 / 965-1, class 6H
What size drill bit for a M2 tap?
To scale section of the tapped hole
Drill options % of thread
| Drill | Inch | mm | Thread | 6H |
|---|---|---|---|---|
| 1/16" | 0.0625 | 1.59 | ✓ | |
| 1.6 mmUse | 0.0630 | 1.60 | ✓ | |
| #52 | 0.0635 | 1.61 | ✓ | |
| 1.65 mm | 0.0650 | 1.65 | ✓ | |
| 1.7 mm | 0.0669 | 1.70 | ✗ | |
| #51 | 0.0670 | 1.70 | ✗ |
75% (orange tick) is the usual target. Hard or gummy metals like stainless are often tapped at 60 to 65% to spare the tap; aluminum, brass and plastic take 75% or a little more. The last column checks the hole against the 6H minor diameter limits (1.57 mm to 1.67 mm).
M2 x 0.4 ISO 261, 965-1, class 6H
| Major diameter | 2 mm / 0.0787 in |
|---|---|
| Pitch | 0.4 mm |
| Pitch diameter (basic) | 1.740 mm |
| Minor diameter 6H | 1.567–1.667 mm |
| Thread-forming tap drill | 1.8 mm 0.0709 in |
Clearance hole ISO 273
For a screw that passes through the part. Normal fit is the default; close fit locates the part more accurately but leaves no room for hole position error.
Hole depth rule of thumb
- 2 mmthread length for full strength in steel (1 × D)
- 3 mmin cast iron or brass (1.5 × D), up to 4 mm in aluminum
- +2 mmextra drill depth below the thread for a plug tap (5 pitches), +0.8 mm with a bottoming tap
Shop notes
M2 x 0.4 is one of the rare metric threads where the inch drill in the drawer is a perfectly good answer. The 1.6 mm drill gives about 77% thread, and a 1/16 (0.0625 in) gives 79%, both inside the 6H minor diameter limits. A #52 sits on the other side at 75%. Pick whichever one is sharp.
The real risk at this size is the tap, not the drill. An M2 tap is fragile, and every extra point of thread is extra torque on it. That is why the useful move in tough material goes up, not down: 1.65 mm leaves about 67% thread and still passes the minor diameter check. Stop there. A 1.7 mm or a #51 drops below 58% and outside the limits, which is a loose thread in a part that has very little thread to spare.
The inch neighbor is #2-56, which is a little larger (0.086 in against 0.0787 in) with a coarser pitch (0.4536 mm against 0.4 mm). The screws look alike in a parts tray and they do not swap. If a tiny screw starts and then stops dead after a turn, check whether you are mixing the two.