The tap drill for an M4 x 0.7 thread is a 3.3 mm drill (0.1299 in), which leaves about 77% of full thread with a cutting tap. The ideal hole for 75% thread is 3.32 mm, and 3.3 mm is the nearest standard metric drill.
| Percent of thread | Ideal hole | Nearest drill | Drill size | Thread achieved |
|---|---|---|---|---|
| 50% | 3.55 mm | 3.5 mm | 3.50 mm / 0.1378 in | 55% |
| 60% | 3.45 mm | 3.5 mm | 3.50 mm / 0.1378 in | 55% |
| 65% | 3.41 mm | 3.4 mm | 3.40 mm / 0.1339 in | 66% |
| 70% | 3.36 mm | 3.4 mm | 3.40 mm / 0.1339 in | 66% |
| 75% | 3.32 mm | 3.3 mm | 3.30 mm / 0.1299 in | 77% |
The drills either side of the target are 11 points of thread apart, so either is a reasonable choice. 3.3 mm (0.1299 in) gives 77% and a stronger but harder-to-tap thread; 3.4 mm (0.1339 in) gives 66% and less tapping torque. On M4 x 0.7 the choice is mostly about tap life in hard materials.
M4 is used for light brackets, cover plates, handles and appliance assemblies. Its basic pitch diameter is 3.55 mm and its tensile stress area is 8.8 mm². A bolt of this size passes through a 4.50 mm normal-fit clearance hole (ISO 273).
Example: M4 x 0.7 at 75% thread
Result: 3.3 mm (0.1299 in), 77% thread
| Major (nominal) diameter | 4.00 mm / 0.1575 in |
|---|---|
| Pitch | 0.7 mm |
| Basic pitch diameter (d − 0.6495·P) | 3.55 mm |
| Basic minor diameter, internal (d − 1.0825·P) | 3.24 mm |
| Tensile stress area | 8.8 mm² |
| Fit | Hole diameter |
|---|---|
| Close | 4.30 mm / 0.1693 in |
| Normal | 4.50 mm / 0.1772 in |
| Loose | 4.80 mm / 0.1890 in |
All Metric coarse sizes:
Use 3.3 mm (0.1299 in). It leaves 77% of full thread with a cutting tap; the ideal 75% hole is 3.32 mm. For an easier-to-tap 50% thread, 3.5 mm (0.1378 in) gives 55%.
3.3 mm is 0.1299 in. The nearest inch drill to the 75% target is #30 (0.1285 in), which gives 81% thread.
A forming tap needs a bigger hole: 3.69 mm for 65% thread, so drill 3.7 mm (0.1457 in). Forming taps work in ductile metals such as aluminum and mild steel.
For M4 x 0.7, ISO 273 gives close fit 4.30 mm, normal fit 4.50 mm and loose fit 4.80 mm. Normal fit suits most bolted joints; close fit locates parts more accurately.
8.8 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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