two paper wheels that go on a bench grinder.....one has grit on it and the other you add a polish to it.....I first saw one at Branson and have had one for about 15 years....just be careful because although i never believed you could get a knife TOO sharp...i was wrong....you can absolutely make one dangerous if you are not careful...especially fixed handled fillet knives
Now my opinion on the 12 volt knife.....Electric Outdoorsman....I used one for probably 10 yrs and it finally wore out....only to find out they no longer made them....it had plenty of power compared to all that have been mentioned and i loved that knife......now i have a berkley....it works pretty good....does not overheat...but it does need a little more power to me

Andy