Gewinde-/Gewindebohrer-Rechner
Determine the correct tap drill size for threading operations. This calculator helps you quickly find the proper pre-drill diameter to ensure accurate threads, proper engagement, and reduced tap breakage risk.
Thread / Tap Drill
Rechner
Typ
M
Tap Drill: 0 mm
Metric formula: Drill ≈ Major Diameter - Pitch
Kurzantwort
- Metrische Gewinde:
Tap Drill ≈ Major Diameter − Pitch - Beispiel:
M10 × 1.5 → 10 − 1.5 = 8.5 mm
Core Formula
D_ approx D_ – P
👉 Wo:
- Ddrill = Tap Drill Diameter (mm)
- Dmajor = Thread Major Diameter (mm)
- P = Thread Pitch (mm)
Anleitung zur Verwendung
- Auswählen thread type (Metric / UNC / UNF)
- Wählen Sie thread size (e.g., M6, M8, M10)
- The calculator automatically outputs:
- Recommended tap drill size
✔ Fast lookup
✔ Engineering reference
✔ Reduces machining errors
Why Tap Drill Size Matters
Correct drill size ensures:
✅ Proper Thread Engagement
- Strong, reliable threads
- Good load distribution
✅ Tool Life
- Prevent tap breakage
- Reduce cutting torque
✅ Thread Quality
- Avoid undersized or oversized threads
- Improve assembly fit
Example
Thread: M8 × 1.25
D_ = 8 – 1.25 = 6.75 mm
👉 Standard drill used: Ø6.8 mm
Common Metric Tap Drill Sizes
| Thema | Pitch | Tap Drill |
|---|---|---|
| M3 | 0.5 | 2,5 mm |
| M4 | 0.7 | 3.3 mm |
| M5 | 0.8 | 4.2 mm |
| M6 | 1.0 | 5.0 mm |
| M8 | 1.25 | 6.8 mm |
| M10 | 1.5 | 8.5 mm |
| M12 | 1.75 | 10.2 mm |
Technische Tipps
Thread Strength vs Ease of Tapping
- Smaller drill → stronger thread but harder tapping
- Larger drill → easier tapping but weaker thread
👉 Typical target: 70–75% thread engagement
Material Consideration
| Material | Empfehlung |
|---|---|
| Aluminium | Slightly smaller drill (better thread grip) |
| Stahl | Standard drill size |
| Edelstahl | Slightly larger drill (reduce torque) |
Tap Type Matters
- Spiral tap → blind holes
- Straight tap → through holes
- Form tap → requires different drill size
Anwendungen
- CNC tapping
- Manual threading
- Automotive & aerospace parts
- Fastener hole preparation
FAQ
What is a tap drill size?
It is the hole diameter drilled before tapping threads.
Why not drill exact thread size?
Threads require material to form the profile, so the hole must be smaller.
Is this formula exact?
It's an engineering approximation. Standard drill charts should be used for precision work.
What about inch threads?
UNC/UNF threads use standard charts rather than simple formulas.
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