It’s basically a tin can with a rag rolled up and pressed in, the rag is soaked with a light oil, in my case it’s wd-40. But any oil that’s thin would work. Putting it on the sole of the plane lets it slide over the wood like ice, super smooth and really helpful, you can feel the cut so much better rather than feeling resistance from the metal on the wood. I’ve had that one for years now, could do with making a new one as the rag is a bit past it, could make a wee video.