M4 Tap Drill Size (M4 x 0.7)
ISO metric coarse · 0.7 mm pitch · ISO 261 / 965-1, class 6H
What size drill bit for a M4 tap?
To scale section of the tapped hole
Drill options % of thread
| Drill | Inch | mm | Thread | 6H |
|---|---|---|---|---|
| #30 | 0.1285 | 3.26 | ✓ | |
| 3.3 mmUse | 0.1299 | 3.30 | ✓ | |
| 3.4 mm | 0.1339 | 3.40 | ✓ | |
| #29 | 0.1360 | 3.45 | ✗ | |
| 3.5 mm | 0.1378 | 3.50 | ✗ |
By material Aluminum, brass, mild steel: 3.3 mm (77%) · Stainless, tool steel: 3.4 mm (66%)
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 (3.24 mm to 3.42 mm).
M4 x 0.7 ISO 261, 965-1, class 6H
| Major diameter | 4 mm / 0.1575 in |
|---|---|
| Pitch | 0.7 mm |
| Pitch diameter (basic) | 3.545 mm |
| Minor diameter 6H | 3.242–3.422 mm |
| Thread-forming tap drill | 3.7 mm 0.1457 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
- 4 mmthread length for full strength in steel (1 × D)
- 6 mmin cast iron or brass (1.5 × D), up to 8 mm in aluminum
- +3.5 mmextra drill depth below the thread for a plug tap (5 pitches), +1.4 mm with a bottoming tap
Shop notes
The 3.3 mm drill is the answer, at about 77% thread. There is no fractional or close inch drill on the page for M4, and the one inch drill that does fit is the #30 (0.1285 in), which runs a bit tight at 81% but stays inside the 6H limits. In soft aluminum that is fine. In steel, a 3.4 mm (66%) is the gentler option and still passes the minor diameter check.
Why the #29 is the wrong habit
The #29 is the drill people grab, because it lives next to the #8-32 taps and M4 and 8-32 are close cousins. In an M4 hole it leaves only 60% thread and falls outside the minor diameter limits. Use the drill that belongs to the thread you are actually tapping.
The two threads are easy to mix up for the same reason. An 8-32 is 0.164 in across with a 0.7938 mm pitch; an M4 is 0.1575 in with a 0.7 mm pitch. That is close enough that one can start in the other's hole and then bind after a turn or so as the pitch difference adds up. If a small screw goes in easily and then locks, stop and check it with a thread gauge before you strip the hole.