Are there any Patent #s ? Anything written or embossed anywhere? Age of glass bottle or jar? From the look of it I would guess maybe some sort of applicator for adhesive or glue. Since you mentioned the wheel is flat. But that is just my guess really have no idea.
If you take off the bottle and fill it with paint, you will have a paint striper. They even used to come with different width wheels. The little protruding metal device was a guide that could be adjusted. Try it out sometime,,,,,,,,,,they work neat !
They all sound like good thoughts. I guess in any case you'd have to wash it real quick after every use.
I don't own it but I know it's abm, probably 30's+. I may have to get it until I find out. I just don't want to spend the $12 on it right now. That's about 4 whole gallons of gas. Of coarse next week it will only be 3. OUCH!!!