[timwilky]

Overtightening isnt going to bend anything. it will strip the thread.

Having stripped the thread you cannot use a tap to recut as there is no material left. so you either have to drill it and tap the next size up or use a helicoil.

Next remember that the drill size is for the root diameter of the thread not the external diameter. you should consult an engineers handbook for the correct drill size for any thread.

Cheap tap and die sets tend to be made from brittle high carbon steel whereas the better ones are made from high speed steel. your taps should come with two possibly 3 taps to each size. the first is tapered to start the thread cutting and the second/third taps take the cut to the final depth. The third tap is usually a plug tap used for blind holes.

Every quarter of a turn back it off to break away the swarf. Always use a proper tap holder, and apply equal load with both hands. I wont go into the physics but I have seen people bang a nut onto a tap and attempt to use a socket wrench. This will induce a bending moment in the tap and lead to it snapping.

Thread restorer files are for small repairs to damaged threads. not to recut.

Also if you intend to use them on you bike bear in mind that Japaneese metric threads sometimes do not use the same pitch as european metric. 10mm being a good example.