/diy/ - Do It Yourself

Bought a tap set and as well as bottoming taps it has what the manufacturer describes as "secondary" and "taper" taps. It doesn't say which is which and both are tapered, one more than the other. I know you're supposed to use a regular tap, which is tapered, before a bottoming tap. What doesn't make sense to me is why it would be a "secondary" tap if it's used first? And which one is the "taper" tap? Is it the most tapered and then you use the secondary one after it, and why would you do that instead of just going straight to the less tapered one?

It's a metric set, so are actual tapered threads for sealing a thing in metric? Meshing them together it doesn't like like one has narrower but full formed teeth towards the end than the other, it just looks like the taper ground into the end goes further.