If you've had to drill out a sheared shaft these can clear remnants from the hole. If the thread is damaged it shaves off the damage. As a last resort drill it larger, tap a new thread and use a larger shaft for the repair (if the assembly will allow it).

Adjustable Silver T-Handle Ratchet Tap Holder Wrench with 5pcs M3-M8 3mm-8mm Machine Screw Thread Metric Plug T-Shaped Tap
4.0

Hi-Spec 20pc Metric Tap & Die Set. Complete M3 to M12 Tapping and Threading Tools with Tap Wrench Accessories
4.0

Gunpla 15pcs Threading Taps Set Metric M3-M12 Alloy Steel Hand Thread Repair Tools with Tap Wrench, HSS Twist Drill Bits Heavy Duty Jobber Drills Kit...
4.0