
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.
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