How To Enlarge an M6 × 1.0 Threaded Hole to an M8 × 1.25?

How To Enlarge an M6 × 1.0 Threaded Hole to an M8 × 1.25?

You may follow the following steps:

🔧 1. Check if there's enough material
Make sure the part has enough wall thickness to handle an M8 thread.

M6 tap drill = Ø5.0 mm

M8 tap drill = Ø6.8 mm

→ So you're only removing about 1.8 mm of material in diameter — generally doable if the original wall isn’t too thin.

🧰 2. Drill the hole larger
Use a 6.8 mm drill bit (preferably HSS).

Ensure the hole is drilled straight and clean.

🔩 3. Tap the hole to M8 × 1.25
Use a M8 × 1.25 tap set (taper, plug, and bottoming if it's a blind hole).

Use cutting fluid or oil for a clean cut.

Tap slowly, backing off periodically to clear chips.

⚠️ Notes:
If the original M6 threads are damaged or you're concerned about strength, you can also consider using a helicoil or thread insert for M8.

For soft metals (e.g., aluminum), consider thread-locking or using inserts if the thread will be loaded.