A Harrowing Disk is used on a farm tractor as an attachment used to work the ground. These disks are available from farmers & farm implement stores. They are great for getting your work surface up off the ground. These can be set on milk crates or have legs welded or bolted to them ... as seen below. The disks come with a small square hole in the middle that is used for mounting the disk on the tool. I've seen these holes plugged up & also left as they are, there isn't that much ash that falls through.