M5 Tap Drill Size (M5 x 0.8)
ISO metric coarse · 0.8 mm pitch · ISO 261 / 965-1, class 6H
What size drill bit for a M5 tap?
To scale section of the tapped hole
Drill options % of thread
| Drill | Inch | mm | Thread | 6H |
|---|---|---|---|---|
| 4.2 mmUse | 0.1654 | 4.20 | ✓ | |
| #19 | 0.1660 | 4.22 | ✓ | |
| 4.3 mm | 0.1693 | 4.30 | ✓ | |
| #18 | 0.1695 | 4.31 | ✓ | |
| 11/64" | 0.1719 | 4.37 | ✗ | |
| #17 | 0.1730 | 4.39 | ✗ | |
| 4.4 mm | 0.1732 | 4.40 | ✗ |
By material Aluminum, brass, mild steel: 4.2 mm (77%) · Stainless, tool steel: 4.3 mm (67%)
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 (4.13 mm to 4.33 mm).
M5 x 0.8 ISO 261, 965-1, class 6H
| Major diameter | 5 mm / 0.1969 in |
|---|---|
| Pitch | 0.8 mm |
| Pitch diameter (basic) | 4.480 mm |
| Minor diameter 6H | 4.134–4.334 mm |
| Thread-forming tap drill | 4.6 mm 0.1811 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
- 5 mmthread length for full strength in steel (1 × D)
- 7.5 mmin cast iron or brass (1.5 × D), up to 10 mm in aluminum
- +4 mmextra drill depth below the thread for a plug tap (5 pitches), +1.6 mm with a bottoming tap
Shop notes
M5 x 0.8 is easy to drill from either side of the Atlantic. The 4.2 mm drill gives about 77% thread, and the #19 (0.1660 in) is practically the same hole at 75%. Neither is a compromise.
If the hole has to be easier on the tap, 4.3 mm or a #18 both land near 67% and still pass the 6H minor diameter check. That is the range to use in stainless. The 11/64 that a fractional set offers is one step too far: at 61% it is outside the limits, and so is everything larger.
The 10-32 look-alike
M5 and #10-32 are the pair that causes the most confusion here. The 10-32 has a 0.7938 mm pitch, almost exactly the 0.8 mm of M5, and its diameter is only a few thousandths smaller (0.190 in against 0.1969 in). A 10-32 screw can thread into an M5 hole and feel normal for several turns, but it engages less of the thread than it should and strips under far less load. Going the other way, an M5 screw in a 10-32 hole is tight from the first turn. If you work on both metric and inch equipment, keep these two in separate bins.