I've got severall of them, and I use them for knives, needles & to start fires with ( using a firesteel ). Small enough to put into your EDC, or sew into your clothing. It works as a emergency blade as well ... .

Works surprisingly well

A nice little whetstone used for refreshing the edge, if your knife is starting to dull. Very fine surface, so don't expect to do much with a rough or chipped edge. Got two different sizes, similar to the one in the pictures. Just be careful with your fingers when handling the smaller one. Would probably be quite nice to mount it on/glue it to something larger to get a better grip on the whetstone.