Metric Tap Drill Chart — ISO Coarse (M1.6 – M56) and Fine (M8 – M52) Threads, mm
Recommended tap drill diameters for ISO metric threads — coarse pitch M1.6 to M56 and fine pitch M8 to M52, with the 5H/6H/7H internal minor-diameter class limits each hole must land between, transcribed row-for-row from the collected chart.
Last updated: 2026-11
Specifications
Tapping cuts an internal thread into a hole that must already be the right size: too small and the tap loads up and snaps, too large and the thread is shallow and strips. The collected chart pairs every ISO metric coarse thread from M1.6 x 0.35 up to M56 x 5.5 with its recommended drill (M6 x 1: 5.00 mm; M10 x 1.5: 8.50 mm; M20 x 2.5: 17.50 mm) and prints, alongside each row, the internal minor-diameter limits for tolerance classes 5H, 6H and 7H plus the common minimum — which is what turns the chart from a rule of thumb into a checkable window: the drilled hole, allowing for drill oversize, should land between the minimum and the chosen class maximum. The old shortcut (tap drill = major diameter minus pitch) still gets you close — it is exact for the coarse series here — but the fine chart shows why the table matters: M10 x 1 takes 9.00 mm while M10 x 1.25 takes 8.80 and M10 x 1.5 takes 8.50, so the pitch you call out on the drawing moves the drill by steps no formula-free shop habit will track. The fine ladder runs M8 x 1 up to M52 x 4. Sizes the source marks * are non-preferred pairings per the standard; two small coarse sizes print no 7H maximum, and one fine row carries an internally inconsistent minimum (both flagged on the table). Coating, tap geometry and the class of thread you need are RFQ decisions, not chart lookups.
| Scope | ISO metric tap drill recommendations — coarse pitch threads M1.6 x 0.35 to M56 x 5.5 (27 rows), fine pitch threads M8 x 1 to M52 x 4 (21 rows); 48 tap/pitch pairs total |
|---|---|
| Recommended drill (mm) | One pre-tapping hole diameter per tap size — coarse examples: M3 x 0.5 → 2.50; M6 x 1 → 5.00; M12 x 1.75 → 10.20; M24 x 3 → 21.00; fine examples: M10 x 1 → 9.00; M12 x 1.5 → 10.50; M20 x 1.5 → 18.50 |
| Class limits printed | Internal minor diameter per row: 5H max, 6H max, 7H max and the 5H/6H/7H common minimum — the drilled hole (less oversize) should fall between the minimum and the selected class maximum |
| Non-preferred sizes | Source marks non-preferred threads with * (e.g. M3.5 x 0.6, M14 x 2, M18 x 2.5, M27 x 3, M39 x 4, M45 x 4.5, M52 x 5) — reproduced as printed |
| Tap geometry / coating / thread class | Not tabulated by the collected chart — per RFQ (state thread class 5H/6H/7H, material to be tapped, and tap type together) |
| Tap Size | Basic Major Dia. (mm) | Thread Pitch (mm) | Minor Dia. 5H max (mm) | Minor Dia. 6H max (mm) | Minor Dia. 7H max (mm) | Minor Dia. 5H/6H/7H min (mm) | Recommended Tap Drill (mm) |
|---|---|---|---|---|---|---|---|
| M1.6 x 0.35 | 1.6 | 0.35 | 1.301 | 1.321 | - | 1.221 | 1.25 |
| M2 x 0.4 | 2 | 0.4 | 1.657 | 1.679 | - | 1.567 | 1.60 |
| M2.5 x 0.45 | 2.5 | 0.45 | 2.113 | 2.138 | - | 2.013 | 2.05 |
| M3 x 0.5 | 3 | 0.5 | 2.571 | 2.599 | 2.639 | 2.459 | 2.50 |
| M3.5* x 0.6 | 3.5 | 0.6 | 2.975 | 3.010 | 3.050 | 2.850 | 2.90 |
| M4 x 0.7 | 4 | 0.7 | 3.382 | 3.422 | 3.466 | 3.242 | 3.30 |
| M5 x 0.8 | 5 | 0.8 | 4.294 | 4.334 | 4.384 | 4.134 | 4.20 |
| M6 x 1 | 6 | 1 | 5.107 | 5.153 | 5.217 | 4.917 | 5.00 |
| M8 x 1.25 | 8 | 1.25 | 6.859 | 6.912 | 6.982 | 6.647 | 6.80 |
| M10 x 1.5 | 10 | 1.5 | 8.612 | 8.676 | 8.751 | 8.376 | 8.50 |
| M12 x 1.75 | 12 | 1.75 | 10.371 | 10.441 | 10.531 | 10.106 | 10.20 |
| M14* x 2 | 14 | 2 | 12.135 | 12.210 | 12.310 | 11.835 | 12.00 |
| M16 x 2 | 16 | 2 | 14.135 | 14.210 | 14.310 | 13.835 | 14.00 |
| M18* x 2.5 | 18 | 2.5 | 15.649 | 15.744 | 15.854 | 15.294 | 15.50 |
| M20 x 2.5 | 20 | 2.5 | 17.649 | 17.744 | 17.854 | 17.294 | 17.50 |
| M22* x 2.5 | 22 | 2.5 | 19.649 | 19.744 | 19.854 | 19.294 | 19.50 |
| M24 x 3 | 24 | 3 | 21.152 | 21.252 | 21.382 | 20.752 | 21.00 |
| M27* x 3 | 27 | 3 | 24.152 | 24.252 | 24.382 | 23.752 | 24.00 |
| M30 x 3.5 | 30 | 3.5 | 26.661 | 26.771 | 26.921 | 26.211 | 26.50 |
| M33* x 3.5 | 33 | 3.5 | 29.661 | 29.771 | 29.921 | 29.211 | 29.50 |
| M36 x 4 | 36 | 4 | 32.145 | 32.270 | 32.420 | 31.670 | 32.00 |
| M39* x 4 | 39 | 4 | 35.145 | 35.270 | 35.420 | 34.670 | 35.00 |
| M42 x 4.5 | 42 | 4.5 | 37.659 | 37.799 | 37.979 | 37.129 | 37.50 |
| M45* x 4.5 | 45 | 4.5 | 40.659 | 40.799 | 40.979 | 40.129 | 40.50 |
| M48 x 5 | 48 | 5 | 43.147 | 43.297 | 43.487 | 42.587 | 43.00 |
| M52* x 5 | 52 | 5 | 47.147 | 47.297 | 47.487 | 46.587 | 47.00 |
| M56 x 5.5 | 56 | 5.5 | 50.646 | 50.796 | 50.996 | 50.046 | 50.50 |
| Tap Size | Basic Major Dia. (mm) | Thread Pitch (mm) | Minor Dia. 5H max (mm) | Minor Dia. 6H max (mm) | Minor Dia. 7H max (mm) | Minor Dia. 5H/6H/7H min (mm) | Recommended Tap Drill (mm) |
|---|---|---|---|---|---|---|---|
| M8 x 1 | 8 | 1 | 7.107 | 7.153 | 7.217 | 6.917 | 7.00 |
| M10 x 1 | 10 | 1 | 9.107 | 9.153 | 9.217 | 8.917 | 9.00 |
| M10* x 1.25 | 10 | 1.25 | 8.859 | 8.912 | 8.982 | 8.647 | 8.80 |
| M12* x 1.25 | 12 | 1.25 | 10.859 | 10.912 | 10.982 | 10.647 | 10.80 |
| M12 x 1.5 | 12 | 1.5 | 10.612 | 10.676 | 10.751 | 10.376 | 10.50 |
| M14* x 1.5 | 14 | 1.5 | 12.612 | 12.676 | 12.751 | 12.376 | 12.50 |
| M16 x 1.5 | 16 | 1.5 | 14.612 | 14.676 | 14.751 | 14.376 | 14.50 |
| M18* x 1.5 | 18 | 1.5 | 16.612 | 16.676 | 16.751 | 16.376 | 16.50 |
| M20 x 1.5 | 20 | 1.5 | 18.612 | 18.676 | 18.751 | 18.376 | 18.50 |
| M20* x 2 | 20 | 2 | 18.135 | 18.210 | 18.310 | 17.835 | 18.00 |
| M22* x 1.5 | 22 | 1.5 | 20.612 | 20.676 | 20.751 | 20.376 | 20.50 |
| M24 x 2 | 24 | 2 | 22.135 | 22.210 | 22.310 | 21.835 | 22.00 |
| M27* x 2 | 27 | 2 | 25.135 | 25.210 | 25.310 | 24.835 | 25.00 |
| M30 x 2 | 30 | 2 | 28.135 | 28.210 | 28.310 | 27.835 | 28.00 |
| M33* x 2 | 33 | 2 | 31.135 | 31.210 | 31.310 | 30.835 | 31.00 |
| M36 x 3 | 36 | 3 | 33.152 | 33.252 | 33.382 | 32.752 | 33.00 |
| M39* x 3 | 39 | 3 | 36.152 | 36.252 | 36.382 | 36.752 | 36.00 |
| M42 x 3 | 42 | 3 | 39.152 | 39.252 | 39.382 | 38.752 | 39.00 |
| M45* x 3 | 45 | 3 | 42.152 | 42.252 | 42.382 | 41.752 | 42.00 |
| M48 x 3 | 48 | 3 | 45.152 | 45.252 | 45.382 | 44.752 | 45.00 |
| M52* x 4 | 52 | 4 | 48.145 | 48.270 | 48.420 | 47.670 | 48.00 |
- Row 17 (M39* x 3): Source prints a 5H/6H/7H minimum minor diameter of 36.752 mm, which sits ABOVE the printed 6H maximum of 36.252 mm — internally inconsistent as printed; verify against the standard before relying on the minimum for M39 x 3.
Materials
- Tap drill selection depends on the material being tapped — softer materials take the tabulated size, harder or gummy alloys may run slightly larger within the class window; state the workpiece material at RFQ
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (Metric Tap Drill Chart — ISO Coarse (M1.6 – M56) and Fine (M8 – M52) Threads, mm) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
How do I use the class-limit columns instead of just reading the drill size, and when does the choice stop being the chart's?
Read the recommended drill as a starting point and the minor-diameter columns as the acceptance window. Drilling is not a precision operation — a twist drill routinely cuts a few hundredths over nominal — so what actually decides whether a tapped hole is good is where the finished hole lands relative to the internal thread limits the chart prints: the common minimum (the floor for every class) and the 5H/6H/7H maximum for the class your mating thread assumes. A hole at or below the minimum starves the thread height; a hole over the class maximum leaves the pitch diameter effectively too loose and the joint rattles or strips. For most general work 6H is the assumed class — the chart's 6H column is the one to check a drill-worn hole against. Where the chart stops helping: abrasive or hardened workpieces, deep holes that need fluted taps and peck cycles, fine pitches in soft alloys that may want the larger end of the window, and any requirement to hit 5H without a reaming operation. Those are process decisions — state the material, thread class and depth at RFQ. Note the flagged rows: M1.6–M2.5 print no 7H maximum, and the M39 x 3 fine row carries a minimum printed above its 6H maximum, an internal inconsistency in the source.
What is the MOQ and lead time for threaded parts and tooling referenced by this chart?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Confirm the exact schedule against quantity, size mix and any tooling items at quotation.
Related knowledge
- Thread-Forming vs Thread-Cutting vs Thread-Rolling Self-Tapping Screws: What the Evidence Settles on Base Material
- Screw Family Selection by Base Material: Wood, Machine and Self-Tapping Threads, Engagement and Coating
- Hex Bolts vs Socket Head Cap Screws: What the Evidence Settles on Strength, Clearance and Cost
Request a Quote
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What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support