Tap Drill Size for M30x3.5

Thread Specifications for M30x3.5

Here are the complete specifications for the M30x3.5 thread:

• Major Diameter: 30.0mm (1.1811″)
• Pitch: 3.5mm
• Tap Drill Size: 26.5mm (1.0433″ / 26.5mm)
• Thread Engagement: ~75% (standard)

How Is the Tap Drill Size Calculated?

The tap drill size for metric threads is calculated using this simple formula:

Tap Drill Diameter = Major Diameter – Pitch

For M30x3.5:

Tap Drill = 30.0mm – 3.5mm = 26.5mm

The recommended tap drill is 26.5mm, which gives approximately 75% thread engagement — the industry standard for most applications.

Why 75% Thread Engagement?

Thread engagement percentage determines how deep the threads are cut. While more might seem better, there is a practical limit:

• 50% engagement provides about 90% of full thread strength — ideal for softer materials or when tap breakage is a concern.
• 75% engagement is the industry standard — excellent strength with reasonable tapping effort. This is what the 26.5mm drill provides for M30x3.5.
• Beyond 83% adds almost no additional strength but significantly increases tapping torque and tap breakage risk.

Pro tip: In aluminum, brass, or other soft materials, 50-60% thread engagement is often preferred to reduce tap breakage. Save 75%+ for steel and harder materials.

Related Thread Sizes

• Tap Drill for M24x3.0 — 21.0mm (0.8268″)
• Tap Drill for M27x3.0 — 24.0mm (0.9449″)