Am busy "tooling up" for my build and I need to buy some taps for threading alu plate, and [possibly] the cores of alu extrusion... and have a few queries please:

I'm guessing that M5, M6, M8, and M12 should cover my needs.

What type of thread are the bolts that most peeps use... metric coarse or metric fine?

I will be using KJN 45x90 Heavy extrusion which has ribbed cores that I think have an internal diameter of 10mm and outer diameter of about 16-17mm. The core-bolts that can be bought from KJN are M12x30, and I think they have two versions of these, one of which is self tapping. Sadly these bolts don't use normal allen-keys £!*%!.

Wanting the frame to be as rigid as possible... Are these M12x30 bolts sufficient, are the self-tapping version sufficent, or would it be better to drill and tap for using bigger bolts?

Sorry about all the little questions, just need some help.

Andy