ISO Metric Thread Drill Tap Size

Overview

Engineering reference data for ISO Metric Thread Drill Tap Size in standard organizations.

Key Formulas

ISO Standard

$ISO \; 9001:2015$

Quality management systems.

ASTM Standard

$ASTM \; E8$

Standard test methods for tension testing.

ANSI Standard

$ANSI/ASME \; B16.5$

Pipe flanges and flanged fittings.

Variables

Symbol	Description	Unit
$ISO$	International Organization for Standardization	—
$ASTM$	American Society for Testing and Materials	—
$ANSI$	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

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:

$D_{\text{tap}} = D - P$

Where:

• $D_{\text{tap}}$ = tap drill diameter
• $D$ = nominal thread diameter
• $P$ = 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.

Interactive Charts

References

• Original Source