A very small, cheap, and handy ceramic sharpening stone. So compact you could even attach (glue is good) this directly to just about any sheath for real easy carry.
The dimensions vary a bit, as you see from the photos. Thickness just a few millimeters.
No idea about the manufacturer but quality-wise these are just as good as any fancy ceramic whetstones.
Pol D.
William W.
Kang C.