Tap Drill Chart

Find the right tap drill size for any thread — UNC, UNF, or Metric

#1-64#530.0595"

#2-56#500.0700"

#3-48#470.0785"

#4-40#430.0890"

#5-40#380.1015"

#6-32#360.1065"

#8-32#290.1360"

#10-24#250.1495"

#12-24#160.1770"

1/4-20#70.2010"

5/16-18F0.2570"

3/8-165/160.3125"

7/16-14U0.3680"

1/2-1327/640.4219"

9/16-1231/640.4844"

5/8-1117/320.5312"

3/4-1021/320.6562"

7/8-949/640.7656"

1-87/80.8750"

1 1/8-763/640.9844"

1 1/4-71 7/641.1094"

1 3/8-61 13/641.2031"

1 1/2-61 11/321.3438"

How to Use a Tap Drill Chart

A tap drill chart tells you what size drill bit to use before tapping a thread. The tap drill creates a hole slightly smaller than the thread's major diameter, leaving enough material for the tap to cut threads into.

What is TPI?

TPI stands for Threads Per Inch. It defines the thread pitch for imperial (inch-based) fasteners. A higher TPI means finer threads. UNC (Unified National Coarse) has fewer threads per inch than UNF (Unified National Fine) for the same nominal size.

UNC vs UNF

UNC (coarse) threads are the most common for general-purpose fastening. They're easier to assemble and more tolerant of damage. UNF (fine) threads provide greater tensile strength and are better for precision applications, vibration resistance, and thin-walled materials.

Metric Threads

Metric threads are specified by diameter and pitch in millimeters (e.g., M8x1.25 = 8mm diameter, 1.25mm pitch). The tap drill size is approximately the major diameter minus the pitch.

75% Thread Engagement

Standard tap drill sizes are calculated for approximately 75% thread engagement, which provides a strong thread while keeping tapping torque manageable. Going beyond 75% adds minimal strength but significantly increases the risk of tap breakage.