How to compare axles from different manufacturers?

Hello guys, as some of you know, I am from Brazil. Here we have some kart axle manufactures, and we import some as well, for example, OTK.
Here in Brazil everybody talks about axle stiffness in numbers. Below I show an example:

Thunder is a local manufacturer brand. They sell Parolin axles as well.

My questions are:
What means these numbers?
What unit is it?
Do you measure axle stiffness in US and Europe like that?
If not, how do you compare stiffness between different axle manufactures?

Other questions…
I heard some axles have different stiffness along their length.

Is it true?
Why axle manufactures do that?
How to select a good mixed stiffness axle?
When harder axles just in the middle are useful?
When harder axles just at the ends are useful?

Have you had an opportunity to read through this? It doesn’t quite answer all of your questions, but it does have valuable information in it.

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I didn´t finish my reading of that post, but I got part of it and I found really interesting that discussion.
But the question of my post above still persist in my mind :slight_smile:
@KartingIsLife, you are in Europe, right? Do you recognize these numbers of the table?

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I’m from Europe, but I live in the US. My uneducated guess is that the numbers are arbitrary and probably a relative scale of some sort.