Metric coarse
Tap drill 1.6 mm for a M2 × 0.4 thread - major Ø 2 mm, pitch 0.4 mm (≈63.5 TPI (converted)).
Profile
| Designation | M2 × 0.4 |
|---|---|
| Major (outside) diameter | 2 mm · 0.0787" |
| Pitch | 0.4 mm · ≈63.5 TPI (converted) |
| Pitch diameter | 1.74 mm · 0.0685" |
| Minor diameter (external) | 1.509 mm · 0.0594" |
| Minor diameter (internal) | 1.567 mm · 0.0617" |
| Recommended tap drill | 1.6 mm · ≈77% thread |
| Clearance hole | Close 2.2 · Normal 2.4 · Loose 2.6 mm |
ISO 273 clearance holes (fine / medium / coarse).
M2 × 0.4 is 2 mm across the crests with a 0.4 mm pitch, which is 63.5 threads per inch. The basic pitch diameter is 1.74 mm and the bolt's minor diameter 1.509 mm, so the thread is 0.246 mm deep on the bolt. The nearest inch size, #1-64 UNC, is 0.15 mm smaller across the crests and its pitch is 0.003 mm finer, so the two do not interchange.
Hole = D − % × 0.0129904 × P, with D = 2 mm and P = 0.4 mm. A smaller hole leaves more thread; the recommended 1.6 mm drill above gives about 77%.
| Thread | Hole (mm) | Hole (in) |
|---|---|---|
| 60% | 1.69 | 0.0665 |
| 65% | 1.66 | 0.0654 |
| 70% | 1.64 | 0.0644 |
| 75% | 1.61 | 0.0634 |
Target preload is 75% of proof load; torque is estimated from T = K · F · d.
| Grade / class | Stress area | Preload | Torque |
|---|---|---|---|
| Class 8.8 | 2.1 mm² | 0.9 kN | 0.4 N·m |
| Class 10.9 | 2.1 mm² | 1.29 kN | 0.5 N·m |
| Class 12.9 | 2.1 mm² | 1.51 kN | 0.6 N·m |
Strengths are ISO 898-1:2013 Table 3 for d ≤ 16 mm. Class 8.8 is size-banded - 580 MPa proof at or below 16 mm, 600 MPa above - while 10.9 and 12.9 hold one value across the range.
The bolt schedule collects the fasteners for one job onto a single sheet - tap drill, wrench size, grade and tightening torque on every line, taken straight from pages like this one. Free schedules hold 3 lines and are saved in this browser only.
For a M2 × 0.4 thread, drill the hole with a 1.6 mm tap drill (1.6 mm - the standard D − P rule) before tapping. That produces roughly 77% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 2 mm and a pitch of 0.4 mm (≈63.5 TPI (converted)).
To pass a M2 × 0.4 bolt through a part rather than thread it, use a clearance hole: Close 2.2 · Normal 2.4 · Loose 2.6 mm.
All values come from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables. See the full reference.
Drill 1.6 mm before tapping M2 × 0.4. That leaves roughly 77% thread engagement, the usual target for a strong hole that still taps cleanly.
M2 × 0.4 is a metric coarse thread. Coarse is the default pitch for M2: when a drawing or supplier says just M2, it means this 0.4 mm pitch.
Drill 2.2 mm for a close fit, 2.4 mm for a normal fit or 2.6 mm for a loose fit (ISO 273). A clearance hole lets the M2 × 0.4 bolt pass through the part instead of threading into it.
Estimated tightening torque for M2 × 0.4 runs from 0.4 N·m (Class 8.8) to 0.6 N·m (Class 12.9), targeting 75% of proof load with a dry nut factor of K = 0.20. Lubricated threads need noticeably less torque.
Closest inch sizes
Nearest standard Unified sizes by major diameter. These are substitutes by size only - the thread forms are not interchangeable, so never run one into the other.
Nearby sizes