Pro Hex Key Assistant
Find the correct Allen wrench, tap drill, and clearance hole size for any metric cap screw — M3 to M16, ISO standard data.
ISO 4762 / DIN 912
M3 – M16
mm / inch toggle
Free to use
Parameters
mm
inch
Results
Required Hex Key (Allen Wrench)
5mm
ISO 4762 · Socket Head · M6
Tap Drill (Pilot)
5.0 mm
For M6×1.0 thread
Clearance Hole
6.6 mm
Normal fit
Full Reference Chart
| Size | Hex Key | Tap Drill | Close Fit | Normal Fit | Large Fit |
|---|
Common Questions
What size hex key does an M6 socket head screw use?
An M6 socket head cap screw requires a 5 mm hex key (Allen wrench) per the ISO 4762 / DIN 912 standard. Note that M6 button and flat head screws use a smaller 4 mm hex key.
What is the tap drill (pilot hole) size for M8?
The standard tap drill for an M8×1.25 metric coarse thread is 6.8 mm. This leaves approximately 75% thread engagement, which is the recommended standard for most materials.
What is the difference between close, normal, and large clearance fit?
Close fit provides precise hole alignment with minimal positional play — used in precision assemblies. Normal fit is the standard general-purpose clearance used in most applications. Large fit offers easier assembly with greater positional tolerance, useful when misalignment is expected.
Do button head screws use the same hex key as socket head cap screws?
No. Button head and flat head cap screws use a smaller hex key than socket head screws of the same diameter. For example, M6 socket head requires a 5 mm key, while M6 button and flat head screws require a 4 mm key. This is due to the lower head profile and reduced drive recess.
What standard does this calculator follow?
Hex key sizes follow ISO 4762 (DIN 912) for socket head cap screws and ISO 7380 for button head screws. Tap drill sizes are based on ISO 68-1 metric coarse thread (standard pitch). Clearance holes follow ISO 273 fit classes.