Taps
 

My wife needs some Christmas list ideas for me and one thing i want is to be able to retap stripped threads in my cars or tap up to the next size but I don’t have any idea how to choose.

I can pick up 2 random screws that use the same 2mm hex and are the same length but the threads are different.
How do I know which is which?

If I have a M3x12mm screw..I know 12mm is the length and I think m3 is a 3.0 hex, right? Is there some secret code that states what style the threads are?

Can you help me pick the sizes that would be appropriate from a 1/16 eRevo to a Xmaxx? Do I need metric and standard? Do you have a link for a set that would cover the sizes I need?

They're for plastic only so hopefully the cheap stuff would work. Thank you!

The M3 refers to the outer nominal diameter of the bolt being 3mm.
2 bolts of the same diameter can have different threads (coarse vs fine thread) just as the can in US standard bolts.