Metric Tap Drill Size Chart (M3–M12): Which Drill Bit Do You Need Before Tapping?
Metric Tap Drill Size Chart (M3–M12): Which Drill Bit Do You Need Before Tapping?
To make an M6 × 1.0 internal thread with a conventional cutting tap, start with a 5.0 mm drill—not a 6.0 mm drill. A tapped hole needs enough material left around its pilot hole for the tap to cut the internal thread. Use this metric reference chart to select a starting drill size, then check the tap manufacturer's recommendations for your material and thread tolerance.
Drill first.
Tap second.
Fit the screw.
Quick workshop reference for M3, M4, M5, M6, M8, M10 and M12 cutting taps.
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Metric tap drill size chart: M3 to M12
These are common starting drill sizes for standard ISO metric coarse threads made with cutting taps. The clearance-hole column is different: it applies when the screw must pass through a separate component without threading into it. All dimensions are in millimetres.
| Thread designation | Pitch (mm) | Tap drill (mm) | Clearance hole (medium, mm) |
|---|---|---|---|
| M3 × 0.5 | 0.50 | 2.5 | 3.4 |
| M4 × 0.7 | 0.70 | 3.3 | 4.5 |
| M5 × 0.8 | 0.80 | 4.2 | 5.5 |
| M6 × 1.0 | 1.00 | 5.0 | 6.6 |
| M8 × 1.25 | 1.25 | 6.8 | 9.0 |
| M10 × 1.5 | 1.50 | 8.5 | 11.0 |
| M12 × 1.75 | 1.75 | 10.2 | 13.5 |
Tap drill vs clearance hole: what is the difference?
A tap drill creates the smaller pilot hole that will later receive internal threads. A clearance hole is larger than the screw's nominal diameter, allowing the screw to pass through one component and engage a separate nut or threaded part. Confusing these two hole types is a common reason a tapping operation fails.
Technical note: The 5.0 mm pilot hole is not threaded yet; drilling can leave faint tool marks, but internal helical threads are created by the cutting tap in the next operation. The 6.6 mm clearance hole also remains smooth and unthreaded; the M6 screw has external threads and passes through with clearance. The illustration is schematic, not a dimensional engineering drawing.
How to calculate the pilot drill size
For a conventional metric cutting tap, a useful workshop estimate is:
M6 × 1.0 → 6.0 − 1.0 = 5.0 mm.
M8 × 1.25 → 8.0 − 1.25 = 6.75 mm → commonly select a 6.8 mm drill.
The result is an approximation that is rounded to an available drill size and must be checked against the selected tap's recommended drill range. It is not a substitute for a process drawing or thread inspection. For fine threads, use the actual pitch: an M8 × 1.0 cutting tap commonly uses a 7.0 mm pilot, not the 6.8 mm coarse-thread pilot.
How to drill and hand-tap a metric hole
| Step | What to do | What to check |
|---|---|---|
| 1 · Confirm | Read the required thread diameter and pitch on the drawing, sample or matching screw. | Do not assume every M8 thread is coarse pitch. |
| 2 · Select | Choose the cutting tap and the corresponding pilot drill from the tap manufacturer's guidance. | Tap type, material, hole depth and thread tolerance. |
| 3 · Secure & drill | Clamp the workpiece, wear suitable eye protection, drill perpendicular to the surface and use appropriate cutting fluid where recommended. | Correct depth; extra room for drill point, tap lead and chips in blind holes. |
| 4 · Deburr | Remove the sharp entry burr and apply a modest lead-in chamfer if the process calls for it. | Do not enlarge the functional thread region unnecessarily. |
| 5 · Start square | Mount the tap in a suitable holder and start it straight, using appropriate lubricant and gentle, even torque. | Do not force a tap that is binding or starting crooked. |
| 6 · Clear & inspect | Manage chips according to tap design and material, withdraw the tap carefully, clean the hole and check with a matching fastener or proper thread gauge. | Production tolerance requires an appropriate GO/NO-GO inspection gauge. |
Cutting taps vs forming taps: do not use the same drill chart
Cutting taps remove material to produce a thread. Forming or roll taps displace ductile material into the thread profile and therefore generally need a larger pilot hole. As one manufacturer example, Vergnano lists an M6 × 1.0 forming-tap drill of 5.55 ± 0.05 mm, compared with the common 5.0 mm cutting-tap pilot. That forming value is product- and process-dependent; do not use it as a universal specification.
| Feature | Cutting tap | Forming tap |
|---|---|---|
| Thread creation | Removes chips | Displaces material |
| Pilot hole | Smaller, often ≈ diameter − pitch | Larger; manufacturer-specific |
| Workpiece suitability | Depends on tool geometry and material | Generally requires sufficiently ductile material |
| Chip management | Important, especially in blind holes | No cutting chips from thread formation |
| What to verify | Tap grade, geometry, tolerance, fluid, depth | Manufacturer's hole range, material, lubrication, tolerance |
Five common mistakes to avoid
Using the screw diameter as the tap drill: an M6 thread does not start with a 6.0 mm cutting-tap pilot. Confusing coarse and fine pitch: M8 × 1.25 and M8 × 1.0 use different cutting-tap pilots. Using a clearance drill: a 6.6 mm M6 clearance hole is not a 5.0 mm M6 cutting-tap hole. Ignoring blind-hole depth: leave space for the tap lead and chips. Assuming a hand-fit proves tolerance: critical production threads need suitable gauges and drawing-based inspection.
Useful OnlyScrews taps, drill bits and tools
The following product pages were checked directly in the connected Shopify catalogue on 30 October 2026 and were active with positive reported inventory. Stock can change. Only the 2.5 mm and 5.0 mm HSS drills below were verified as matching tap-drill products; do not substitute other drill diameters for the remaining chart entries.
Frequently asked questions
What drill bit do I need for an M3 tap?
For a conventional cutting tap making M3 × 0.5 coarse threads, a 2.5 mm pilot drill is a common starting recommendation.
What is the correct tap drill for M4, M5 and M6?
For common coarse cutting taps: M4 × 0.7 → 3.3 mm; M5 × 0.8 → 4.2 mm; M6 × 1.0 → 5.0 mm.
Can I use a 6 mm drill bit to tap an M6 hole?
Not for a standard M6 × 1.0 cutting-tap hole. A 6 mm hole is close to the nominal screw diameter and would leave insufficient material for the intended internal thread.
Is a tap drill the same as a clearance drill?
No. A tap drill leaves material for internal threads; a clearance drill is larger so a screw can pass through a separate part without threading into it.
Why is the drill size different for a forming tap?
A forming tap displaces metal rather than cutting chips. It generally needs a larger starting hole; consult the specific forming-tap manufacturer and workpiece-material chart.
Can I use the M8 coarse chart for M8 × 1.0 fine pitch?
No. M8 × 1.25 commonly uses a 6.8 mm cutting-tap drill; M8 × 1.0 commonly uses 7.0 mm. Confirm the pitch before drilling.
Related OnlyScrews guides
First identify the thread pitch using Metric Screw Thread Pitch: How to Measure It. If the hole is already stripped, see How to Install a Helicoil Thread Insert. For screw size basics, see How to Measure Screw Diameter.
Six-step hand-tapping workflow
Technical sources and verification
Reference values and limitations were cross-checked on 31 October 2026 against these sources:
- TR Fastenings — Tapping sizes and clearance holes (M3–M12 tap and clearance values).
- Sandvik Coromant — Tapping operation tips (coolant, tool alignment and process considerations).
- Sandvik Coromant — CoroTap 300 (spiral flute taps and blind-hole chip evacuation).
- Vergnano — Drill size for forming taps (M6 forming-tap hole size and material-dependent limits).
- ISO 261 — ISO metric screw threads, general plan (thread pitch context, not a drill-size specification).