The tap drill for M6 x 1 is 5.0 mm (0.1969 in), which gives about 77% of full thread depth. The exact 75% hole is 0.1979 in (5.03 mm). The table lists every number, letter, fractional and metric drill that gives between 55% and 90% thread, so you can work from the bits you own.
| Drill | Type | in | mm | Thread | Note |
|---|---|---|---|---|---|
| 4.9 mm | metric | 0.1929 | 4.90 | 85% | deep, hard to tap |
| #10 | number | 0.1935 | 4.91 | 84% | deep, hard to tap |
| #9 | number | 0.1960 | 4.98 | 79% | |
| 5 mm | metric | 0.1969 | 5.00 | 77% | chart drill |
| #8 | number | 0.1990 | 5.05 | 73% | |
| 5.1 mm | metric | 0.2008 | 5.10 | 69% | |
| #7 | number | 0.2010 | 5.11 | 69% | |
| 13/64" | fraction | 0.2031 | 5.16 | 65% | easier to tap |
| #6 | number | 0.2040 | 5.18 | 63% | easier to tap |
| 5.2 mm | metric | 0.2047 | 5.20 | 62% | easier to tap |
About the M6 x 1 thread
M6 x 1 is the metric equivalent of 1/4-20 in everyday use: furniture connector bolts and threaded inserts in flat-pack furniture, cage nuts in European equipment racks, aluminium extrusion T-nuts, larger VESA mounts and many brackets and handles. In woodworking jigs outside North America, M6 knobs and inserts do the job 1/4-20 does in the US.
The tap drill is a round 5 mm (diameter minus pitch), giving a thread just over 75%. That makes M6 one of the easiest threads to get right, provided you have M6 x 1 and not the fine M6 x 0.75, which is rare outside special fittings.
M6 x 1 thread dimensions
| Dimension | Value | Also |
|---|---|---|
| Nominal diameter | 6 mm | 0.2362 in |
| Pitch | 1 mm | 25.40 threads per inch equivalent |
| Basic pitch diameter | 5.350 mm | 0.2106 in |
| Basic minor diameter (nut) | 4.917 mm | 0.1936 in |
| Tensile stress area | 20.12 mm² | 0.0312 in² |
Clearance hole for M6
The tapped hole is in the part that holds the thread; the part being clamped gets a clearance hole the bolt passes through. For M6 a normal fit is 6.6 mm. Never drill the clearance part with the tap drill: the screw will not pass.
| Fit | Drill | Diameter |
|---|---|---|
| Close (ISO 273 fine) | 6.4 mm | 0.2520 in |
| Normal (ISO 273 medium) | 6.6 mm | 0.2598 in |
| Loose (ISO 273 coarse) | 7 mm | 0.2756 in |
How deep to drill a blind M6 x 1 hole
| Part material | Full thread wanted | Drill depth (full diameter) | Depth to drill tip (118°) |
|---|---|---|---|
| Steel or cast iron (1 × diameter) | 6.0 mm | 13.0 mm | 14.5 mm |
| Aluminium or brass (2 × diameter) | 12.0 mm | 19.0 mm | 20.5 mm |
Wrench size and torque for M6
- Hex bolt or nut: 10 mm wrench (ISO)
- Socket head cap screw (ISO 4762): 5 mm hex key
| Bolt grade | Dry | Lubricated |
|---|---|---|
| Class 8.8 | 10.5 N·m (7.7 ft-lb) | 7.9 N·m |
| Class 10.9 | 15.0 N·m (11.1 ft-lb) | 11.3 N·m |
| Class 12.9 | 17.6 N·m (13.0 ft-lb) | 13.2 N·m |
Threads easily mistaken for M6 x 1
| Thread | Diameter (in) | Diameter (mm) | Pitch |
|---|---|---|---|
| M6 x 1 (this page) | 0.2362 | 6.00 | 1 mm (25.4 TPI) |
| 1/4-20 UNC | 0.2500 | 6.35 | 20 TPI (1.27 mm) |
| 1/4-28 UNF | 0.2500 | 6.35 | 28 TPI (0.91 mm) |
Tips for tapping M6 x 1
- M6 and 1/4-20 are 0.236 and 0.250 in across. A 1/4-20 bolt will not go into an M6 hole; an M6 bolt rattles in a 1/4-20 hole and strips it.
- For M6 threaded inserts in hardwood or MDF, drill the insert maker’s hole size (often 8 to 8.5 mm), not the tap drill.
- An M6 socket head cap screw takes a 5 mm hex key; an M6 hex bolt needs a 10 mm wrench.
- If an M6 thread in a flat-pack fitting strips, a slightly longer screw or a new insert is a better fix than drilling out to M8.
Frequently asked questions
What size drill bit for an M6 x 1 tap?
5.0 mm, which gives about 77% thread. The exact 75% size is 0.1979 in (5.03 mm).
How deep should a blind M6 x 1 hole be?
For a full thread of 1 × diameter in steel, drill about 13.0 mm at full diameter with a plug tap, or 14.5 mm to the drill tip; in aluminium, about 19.0 mm.
What size drill for an M6 tap in inches?
#9 (0.196 in, 4.98 mm) is almost exactly 5 mm. 13/64 in (0.203 in) gives a shallower thread that is still usable in soft metals.
Can I use M6 instead of 1/4-20?
Only if both parts are M6. The diameters and pitches differ (1 mm against 1.27 mm), so the two cannot be mixed in the same hole.
Sources and method
Every dimension and percentage on this page is computed from the formulas listed, not copied from another chart. Values are basic (nominal); real parts are made to tolerance classes (2A/2B for inch, 6g/6H for metric).
- ASME B1.1 and FED-STD-H28/2B (Unified inch), ISO 68-1 and ISO 261 (metric): basic thread profile and stress area formulas.
- Machinery’s Handbook (Industrial Press): percentage-of-thread relation used by our tap drill size calculator.
- ASME B94.11M twist drill series (number, letter, fractional); 0.1 mm metric drill steps.
- ISO 273 metric clearance holes; inch close, normal and loose fits as published in the ASME B18.2.8 clearance classes.
- SAE J429 and ISO 898-1 proof strengths; T = K × D × F torque relation (see our bolt torque chart for the full method).
- Wrench and hex key sizes: ASME B18.2.1, ASME B18.3, ASME B18.6.3, ISO 4014/4017, DIN 933 and ISO 4762 values as widely published.
More thread and fastener tools
- All thread and fastener charts
- UNC and UNF thread chart
- Metric thread pitch chart
- Tap drill chart (inch and metric)
- Clearance hole chart
- Nail size chart
- Wood screw size chart
- Lag screw pilot hole chart
- Bolt torque chart
- Wrench size chart
- Drill bit size chart
- Thread engagement chart
- Nail gun nail sizes by gauge
- Screw and nail size calculator
- Tap drill size calculator
- Clearance hole size calculator
- Tapped hole depth calculator
Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.