This is a threaded adapter for the Dremel to sharped knifes and/or lawn mower blades. There are two different angles for sharpening. I printed it in ABS and used acetone to smooth the threads in order to make it easier to put on.
Update: I printed this on its side without any supports or a raft. I used ABS, and I would advise if you do as well then you should scale it by at least 1%(varies with different printers) to compensate for shrinkage. The threads will be fairly tight, so if that is a concern then scale it just a little more (maybe 1.5%-2%).