What drill bit size to use?

[KatieandDad]

Why not just pick up a bit of scrap ally and try tapping a few holes.

[Lavcat]

Originally Posted by KatieandDad

Why not just pick up a bit of scrap ally and try tapping a few holes.

Because I don't have a tap. I don't have any taps at all, cutting or Thredfloer. I've used a tap but not in a long time. Of couse I intend first to try various methods in less good aluminum before I start in on the real panel.

[AndrewT]

The UK has a variety of cheap carbon steel tapping and threading kits.
Both metric and imperial thread forms in a wide variety of sizes.
This is the cheapest way to start tapping aluminium.
Do not expect carbon taps to tap any of the hard materials.
Carbon is a bit brittle, so you must learn to tap accurately without abusing the tap.
Cheap carbon will not be as accurate as proper taps.

If you require steel tapping and or a specialized hole size or thread form, then you can buy the expensive set of three taps. tapered, second and plug tap. These can also be bought in the various tap types and individually they are not anywhere near cheap. You will weep if you break one.