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"Glen's" grit system is easy, I can shave well off the Norton 8k, the Naniwa SS 8k, or the Shapton GS 8k
I also know that a Norton 4k is lower in grit than a Norton 8k and a Naniwa SS 5k is lower...

The Norton is rated using the Japanese system, if you want to search it out, right here on SRP you are going to find an e-mail from Norton stating exactly that.. Easier than that is to hone a razor...