Re-tapping M3 to 6-32 UNC
The tap drill for a m3 is 2.5mm or .0984" the tap for a #6 is .1065" these are fairly close in size but the #6 is larger so there would be some thread depending on the strength needed there may be enough to do the project it would be worth a try since the fasteners are "custom". I would give taping a try to see if there will be enough thread to do the job I don't have any metric taps to measure the depth of the thread for a m3.