Shapton KUROMAKU "Green" Waterstone
These Kuromaku/Professional series stones are very fast cutting and long-lasting, offering nice sharpening feedback while still being very hard so they resist dishing nicely. Note that these are splash-and-go, so do not soak these stones.
These stones come in a convenient plastic case that also doubles as a stone holder, though the affordable Naniwa universal/adjustable stone holder also works fine for these stones and will certainly be more stable and secure.
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210mm x 70mm, 15mm thick.