How to Tap Internal Threads & Cut External Threads
🕒 3 Minutes Reading Time -
Mastering Metalwork: How to Create Internal & External Threads
Threading and tapping are essential skills in metalworking. Whether you're repairing a stripped bolt hole or creating a custom assembly, precision threads ensure a strong, reliable connection. In this guide, you’ll learn how to cut external threads, tap internal threads, choose the correct drill size, and which Batavia tools help you achieve professional results.
What you'll learn
Why threading matters
Threads are the foundation of countless mechanical connections. A well-cut thread ensures strength, precision and long-term reliability. Poorly cut threads, however, can lead to weak joints, misalignment or even broken taps.
Tools & drill size chart
To create clean, accurate threads, you need the right combination of hand tools, power tools and accessories.
| Thread Size | Pilot Hole Diameter |
|---|---|
| M3 | 2.5 mm |
| M4 | 3.3 mm |
| M5 | 4.2 mm |
| M6 | 5.0 mm |
| M8 | 6.8 mm |
| M10 | 8.5 mm |
| M12 | 10.2 mm |
Essential tools & accessories
- Tap and die set (including taper, plug and bottoming taps)
- Tap wrench for controlled internal threading
- High-speed steel (HSS) metal drill bits
- Cutting oil to reduce friction and prevent overheating
- Die and die stock for external threads
Recommended Batavia tools
18V Cordless Drill Driver
- Ideal for drilling precise pilot holes
- Speed control ensures clean, accurate drilling
18V Combi Drill
- Suitable for metalwork when hammer mode is switched off
- Reliable for drilling and light fastening tasks
Impact Drivers
- Great for tightening bolts
- Not recommended for drilling fine pilot holes
Rotary Hammers
- Not suitable for metal threading or tapping
Step-by-step: threading & tapping
- Mark & center punch. Mark the hole location and use a center punch to prevent wandering.
- Drill the pilot hole. Use the correct drill size (e.g., 5.0 mm for M6) with a Batavia Cordless Drill.
- Deburr & countersink. Lightly chamfer the hole so the tap starts smoothly.
- Secure the workpiece. Clamp the metal firmly in a vice.
- Apply cutting oil. Essential for cooling and smooth cutting.
- Tap the internal thread. Turn the tap slowly: half-turn forward, quarter-turn back to break the chip.
- Cut external threads. Chamfer the rod, align the die squarely and apply steady pressure while lubricating.
- Test the fit. Use a matching bolt or nut to confirm smooth threading.
Safety tip: Never force a tap. If resistance increases sharply, back out immediately to avoid breakage.
Pro tips for perfect threads
- Keep the tap or die perfectly square to avoid crooked threads
- Use slower speeds and more lubrication on stainless steel
- Break the chip frequently to prevent clogging
- Use a high-quality drill driver for maximum control
FAQ: Threading & Tapping
What is the difference between threading and tapping?
Threading creates external threads using a die, while tapping creates internal threads using a tap.
Why is cutting oil important?
It reduces friction, prevents overheating and helps produce cleaner, more accurate threads.
What causes taps to break?
Most tap breakages occur due to misalignment, too-small pilot holes or failing to break the chip regularly.
Ready to start threading?
With the right preparation, correct drill sizes and a reliable Batavia drill, you can create strong, precise threads for any metalworking project. Whether you're tapping an M4 hole or cutting an M12 thread, quality tools make all the difference.