M16 Tap Drill Size (M16 x 2.0)
ISO metric coarse · 2 mm pitch · ISO 261 / 965-1, class 6H
What size drill bit for a M16 tap?
To scale section of the tapped hole
Drill options % of thread
| Drill | Inch | mm | Thread | 6H |
|---|---|---|---|---|
| 35/64" | 0.5469 | 13.89 | ✓ | |
| 14 mmUse | 0.5512 | 14.00 | ✓ | |
| 9/16" | 0.5625 | 14.29 | ✗ | |
| 14.5 mm | 0.5709 | 14.50 | ✗ |
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 (13.83 mm to 14.21 mm).
M16 x 2 ISO 261, 965-1, class 6H
| Major diameter | 16 mm / 0.6299 in |
|---|---|
| Pitch | 2 mm |
| Pitch diameter (basic) | 14.701 mm |
| Minor diameter 6H | 13.835–14.210 mm |
| Thread-forming tap drill | 15 mm 0.5906 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
- 16 mmthread length for full strength in steel (1 × D)
- 24 mmin cast iron or brass (1.5 × D), up to 32 mm in aluminum
- +10 mmextra drill depth below the thread for a plug tap (5 pitches), +4 mm with a bottoming tap
Shop notes
For M16 x 2 the choice is short. The 14 mm drill gives about 77% thread, and only one inch drill also passes the 6H minor diameter check: the 35/64 (0.5469 in, 81%). It cuts a fuller thread than the metric drill and asks more of the tap, which at this size is a lot of torque, but it is a legitimate substitute.
The 9/16 is the drill people expect to work, because it is a round size close to the hole. It is not: at 0.5625 in it leaves about 66% thread and falls outside the limits. The 14.5 mm is further out still. On a thread this large an undersized engagement is easy to miss by eye, so check the hole with a plug gauge or a known good bolt rather than trusting the feel of the tap.
The inch thread nearest in size is 5/8-11, and it is close: 0.625 in against 0.6299 in. The pitches are not (2.3091 mm against 2 mm), so the two do not swap even though they look alike on a shelf. A 5/8-11 bolt that starts and then binds within a turn or two in a hole that looks right is a good reason to suspect the hole was tapped M16.