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Hmm like stefan told you they are all different but mine i guess is lv 3 out of 5, but i have to say it is not as fine as Jnat lv 3

You can try them out :)
I have 5 of them from him and i will not even use them on my knifes. I have huge Iyo stone too but i dont like it ether.
I feel like Iyo stones contain to much sand, but...

The video is for knifes Iyo Nagura is to coarse thats why it sound that way, i will not even recommend it for knifes.
But i think you can use Asano Naguras on C12K why not, but they are coarse then...