The tap drill for M10 x 1.5 is 8.5 mm (0.3346 in), which gives about 77% of full thread depth. The exact 75% hole is 0.3362 in (8.54 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 |
|---|---|---|---|---|---|
| 8.3 mm | metric | 0.3268 | 8.30 | 87% | deep, hard to tap |
| 21/64" | fraction | 0.3281 | 8.33 | 85% | deep, hard to tap |
| 8.4 mm | metric | 0.3307 | 8.40 | 82% | deep, hard to tap |
| Q | letter | 0.3320 | 8.43 | 80% | deep, hard to tap |
| 8.5 mm | metric | 0.3346 | 8.50 | 77% | chart drill |
| 8.6 mm | metric | 0.3386 | 8.60 | 72% | |
| R | letter | 0.3390 | 8.61 | 71% | |
| 8.7 mm | metric | 0.3425 | 8.70 | 67% | easier to tap |
| 11/32" | fraction | 0.3438 | 8.73 | 65% | easier to tap |
| S | letter | 0.3480 | 8.84 | 60% | easier to tap |
About the M10 x 1.5 thread
M10 x 1.5 is the coarse 10 mm thread on machinery and structural-steel bolts, engine mounts, heavy brackets and furniture and shelving systems. Fine versions are common on vehicles: M10 x 1.25 on many bolts and fittings, and M10 x 1 on brake banjo bolts and bleed fittings for many makes. A 10 mm bolt also tends to be confused with a 3/8 in one, which is only 0.019 in smaller.
For the coarse thread the chart drill is 8.5 mm, exactly diameter minus pitch. The fine-thread rows below give 8.75 mm for M10 x 1.25 (an 8.8 mm bit) and 9.0 mm for M10 x 1.
M10 x 1.5 thread dimensions
| Dimension | Value | Also |
|---|---|---|
| Nominal diameter | 10 mm | 0.3937 in |
| Pitch | 1.5 mm | 16.93 threads per inch equivalent |
| Basic pitch diameter | 9.026 mm | 0.3553 in |
| Basic minor diameter (nut) | 8.376 mm | 0.3298 in |
| Tensile stress area | 57.99 mm² | 0.0899 in² |
| Fine thread M10 x 1.25: tap drill | 8.75 mm | 77% thread |
| Fine thread M10 x 1: tap drill | 9.00 mm | 77% thread |
Clearance hole for M10
The tapped hole is in the part that holds the thread; the part being clamped gets a clearance hole the bolt passes through. For M10 a normal fit is 11 mm. Never drill the clearance part with the tap drill: the screw will not pass.
| Fit | Drill | Diameter |
|---|---|---|
| Close (ISO 273 fine) | 10.5 mm | 0.4134 in |
| Normal (ISO 273 medium) | 11 mm | 0.4331 in |
| Loose (ISO 273 coarse) | 12 mm | 0.4724 in |
How deep to drill a blind M10 x 1.5 hole
| Part material | Full thread wanted | Drill depth (full diameter) | Depth to drill tip (118°) |
|---|---|---|---|
| Steel or cast iron (1 × diameter) | 10.0 mm | 20.5 mm | 23.1 mm |
| Aluminium or brass (2 × diameter) | 20.0 mm | 30.5 mm | 33.1 mm |
Wrench size and torque for M10
- Hex bolt or nut: 16 mm wrench (ISO), 17 mm on DIN 933 and older bolts
- Socket head cap screw (ISO 4762): 8 mm hex key
| Bolt grade | Dry | Lubricated |
|---|---|---|
| Class 8.8 | 50.5 N·m (37.2 ft-lb) | 37.8 N·m |
| Class 10.9 | 72.2 N·m (53.3 ft-lb) | 54.1 N·m |
| Class 12.9 | 84.4 N·m (62.2 ft-lb) | 63.3 N·m |
Threads easily mistaken for M10 x 1.5
| Thread | Diameter (in) | Diameter (mm) | Pitch |
|---|---|---|---|
| M10 x 1.5 (this page) | 0.3937 | 10.00 | 1.5 mm (16.9 TPI) |
| M10 x 1.25 | 0.3937 | 10.00 | 1.25 mm (20.3 TPI) |
| M10 x 1 | 0.3937 | 10.00 | 1 mm (25.4 TPI) |
| 3/8-16 UNC | 0.3750 | 9.52 | 16 TPI (1.59 mm) |
| 3/8-24 UNF | 0.3750 | 9.52 | 24 TPI (1.06 mm) |
Tips for tapping M10 x 1.5
- Before re-tapping anything on a vehicle, confirm the pitch with a gauge; brake and fuel fittings are safety parts, so replace damaged ones rather than re-tapping.
- An M10 hex bolt needs a 16 mm wrench (ISO) or 17 mm (DIN and older bolts); an M10 socket head cap screw takes an 8 mm hex key.
- 21/64 in (0.328 in, 8.33 mm) gives too deep a thread; the nearest inch drill to 8.5 mm is letter Q (0.332 in) or R (0.339 in).
- For a 10 mm tap in steel use a tap wrench at least 250 mm long and plenty of cutting fluid.
Frequently asked questions
What size drill bit for an M10 x 1.5 tap?
8.5 mm, which gives about 77% thread. The exact 75% size is 0.3362 in (8.54 mm).
How deep should a blind M10 x 1.5 hole be?
For a full thread of 1 × diameter in steel, drill about 20.5 mm at full diameter with a plug tap, or 23.1 mm to the drill tip; in aluminium, about 30.5 mm.
Is M10 the same as 3/8?
No. 3/8 in is 9.53 mm; M10 is 10 mm. 3/8-16 UNC and M10 x 1.5 also differ in pitch (1.59 mm against 1.5 mm).
What size drill for an M10 x 1.25 tap?
8.75 mm (10 minus 1.25); an 8.8 mm bit is the usual choice.
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.