The tap drill for an M2 x 0.4 thread is a 1.6 mm drill (0.0630 in), which leaves about 77% of full thread with a cutting tap. The ideal hole for 75% thread is 1.61 mm, and 1.6 mm is the nearest standard metric drill.
| Percent of thread | Ideal hole | Nearest drill | Drill size | Thread achieved |
|---|---|---|---|---|
| 50% | 1.74 mm | 1.75 mm | 1.75 mm / 0.0689 in | 48% |
| 60% | 1.69 mm | 1.7 mm | 1.70 mm / 0.0669 in | 58% |
| 65% | 1.66 mm | 1.65 mm | 1.65 mm / 0.0650 in | 67% |
| 70% | 1.64 mm | 1.65 mm | 1.65 mm / 0.0650 in | 67% |
| 75% | 1.61 mm | 1.6 mm | 1.60 mm / 0.0630 in | 77% |
The drills either side of the target are 10 points of thread apart, so either is a reasonable choice. 1.6 mm (0.0630 in) gives 77% and a stronger but harder-to-tap thread; 1.65 mm (0.0650 in) gives 67% and less tapping torque. On M2 x 0.4 the choice is mostly about tap breakage.
M2 holds circuit boards, fans, small hinges and camera parts, where a screw has to be small but still take a driver. Its basic pitch diameter is 1.74 mm and its tensile stress area is 2.1 mm². A bolt of this size passes through a 2.40 mm normal-fit clearance hole (ISO 273).
Example: M2 x 0.4 at 75% thread
Result: 1.6 mm (0.0630 in), 77% thread
| Major (nominal) diameter | 2.00 mm / 0.0787 in |
|---|---|
| Pitch | 0.4 mm |
| Basic pitch diameter (d − 0.6495·P) | 1.74 mm |
| Basic minor diameter, internal (d − 1.0825·P) | 1.57 mm |
| Tensile stress area | 2.1 mm² |
| Fit | Hole diameter |
|---|---|
| Close | 2.20 mm / 0.0866 in |
| Normal | 2.40 mm / 0.0945 in |
| Loose | 2.60 mm / 0.1024 in |
All Metric coarse sizes:
Use 1.6 mm (0.0630 in). It leaves 77% of full thread with a cutting tap; the ideal 75% hole is 1.61 mm. For an easier-to-tap 50% thread, 1.75 mm (0.0689 in) gives 48%.
1.6 mm is 0.0630 in. The nearest inch drill to the 75% target is #52 (0.0635 in), which gives 74% thread.
A forming tap needs a bigger hole: 1.82 mm for 65% thread, so drill 1.8 mm (0.0709 in). Forming taps work in ductile metals such as aluminum and mild steel.
For M2 x 0.4, ISO 273 gives close fit 2.20 mm, normal fit 2.40 mm and loose fit 2.60 mm. Normal fit suits most bolted joints; close fit locates parts more accurately.
2.1 mm², from As = π/4 × (d − 0.9382 × P)². Multiply it by the bolt material's proof or tensile strength to get the load the thread can carry.
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