Tap & Drill Size Chart

How to Use This Chart

Tap Drill Size

The tap drill creates the hole that will be tapped (threaded). The tap drill is sized to leave approximately 75% thread engagement, which is the standard for most applications. A 75% thread provides nearly the same strength as 100% thread engagement but requires significantly less tapping torque and reduces tap breakage.

Clearance Drill Size

The clearance drill creates a hole large enough for the bolt or screw to pass through freely without engaging the threads. Use the clearance drill size for through-holes where you don't want threads.

UNC vs UNF

UNC (Unified National Coarse) threads are the default for general-purpose fastening. They're easier to assemble, more tolerant of minor damage, and less likely to cross-thread. Use UNC unless you have a specific reason not to.

UNF (Unified National Fine) threads have a smaller pitch, which provides higher tensile strength in the same diameter, better vibration resistance, and finer adjustment. Common in automotive, aerospace, and precision applications.

Metric Thread Designation

Metric threads are designated as M[diameter]×[pitch] — for example, M8×1.25 is an 8mm diameter thread with a 1.25mm pitch. When only one pitch is listed for a diameter, it's the standard (coarse) pitch. Fine-pitch variants are listed separately.

CNC Tapping Tips

• Use a peck-tapping cycle (G84) for blind holes to clear chips
• For CNC rigid tapping, ensure your spindle speed and feed rate are synchronized: feed (IPM) = RPM / TPI
• Use cutting oil or tapping fluid — dry tapping dramatically reduces tap life
• For difficult materials, consider using a roll-form (thread-forming) tap instead of a cutting tap