ISO Metric Thread Drill Tap Size
Reference data and engineering information about iso metric thread drill tap size for standard organizations applications.
Overview
Engineering reference data for ISO Metric Thread Drill Tap Size in standard organizations.
Key Formulas
ISO Standard
Quality management systems.
ASTM Standard
Standard test methods for tension testing.
ANSI Standard
Pipe flanges and flanged fittings.
Variables
| Symbol | Description | Unit |
|---|---|---|
| International Organization for Standardization | — | |
| American Society for Testing and Materials | — | |
| American National Standards Institute | — |
ISO Metric Thread Clearance Holes and Tap Drill Sizes
The following table provides standard clearance hole diameters (for bolt pass-through) and recommended tap drill sizes for ISO metric threads per ISO 724.
Clearance Hole and Tap Drill Reference Table
Nominal Diameter(mm) | Pitch(mm) | Clearance Hole (Fine)(mm) | Clearance Hole (Medium)(mm) | Clearance Hole (Coarse)(mm) | Tap Drill Size(mm) |
|---|---|---|---|---|---|
| 1.6 | 0.35 | 1.7 | 1.8 | 2 | — |
| 1.8 | 0.35 | — | 2 | — | — |
| 2 | 0.4 | 2.2 | 2.25 | 2.6 | — |
| 2.2 | 0.45 | — | 2.45 | — | — |
| 2.5 | 0.45 | 2.7 | 2.8 | 3.1 | — |
| 3 | 0.5 | 3.2 | 3.35 | 3.6 | — |
| 3.5 | 0.6 | — | 3.9 | — | — |
| 4 | 0.7 | 4.3 | 4.5 | 4.8 | — |
| 4.5 | 0.75 | — | 5 | — | — |
| 5 | 0.8 | 5.3 | 5.5 | 5.8 | 4.2 |
| 6 | 1 | 6.4 | 6.5 | 7 | 5 |
| 7 | 1 | 7.4 | 7.8 | 8 | 6 |
| 8 | 1.25 | 8.4 | 9 | 10 | 6.75 |
| 10 | 1.5 | 10.5 | 11 | 12 | 8.5 |
| 12 | 1.75 | 13 | 14 | 15 | 10.25 |
| 16 | 2 | 17 | 18 | 19 | 14 |
| 20 | 2.5 | 21 | 22 | 24 | 17.5 |
| 24 | 3 | 25 | 26 | 28 | 21 |
| 30 | 3.5 | 31 | 32 | 35 | 26.5 |
Source: ISO 724
Clearance Hole Fit Categories
Clearance holes are categorized by fit tolerance relative to the bolt:
| Fit Type | Description | Application |
|---|---|---|
| Fine | Close fit, minimal clearance | Precision alignment required |
| Medium | Standard fit, moderate clearance | General purpose applications |
| Coarse | Loose fit, maximum clearance | Easy assembly, misalignment tolerance |
Tap Drill Selection Notes
The tap drill size produces approximately 75% thread depth using the standard formula:
Where:
- = tap drill diameter
- = nominal thread diameter
- = thread pitch
This formula is applied for sizes M5 and larger in the table above. For smaller metric sizes, consult standard drill charts or use the nearest available standard drill size.