It's a shop-made horizontal disk grinder that I built several years from an old foot massager that I picked up from a secondhand store. The disks have different grits of paper glued to them with good old Elmer's Rubber Cement to make replacement easy. They mount to the unit by slipping over a couple of metal dowels which hold them in place while the unit spins. I have a dimmer switch to control the speed and the direction of rotation is reversible. It works great for grinding flats and for final sharpening as well. It's one of the most useful tools in my shop.