Do they have any branding, codes or numbers? If they’re a brand,
look for that brands website. If they have other numbers, like 3/0
or 20micron, then you should be able to find a comparison table on
the internet - I’m in a rush, so I can’t find you a link.
Bear in mind that there are no objective rules about abrasion - so
long as you use progressively finer abrasives, you’ll be fine, and
you can usually tell by touch. If in doubt, play around with some
metal, and you’ll soon see.