Needed a way to size and smooth the inside of a circular pla printed part, sand paper mostly just gums up from heat... this doesn't. The inside hole is 1/4 inch for a piece of allthread with nuts on either side.. seems to work well.. the blades are maybe a little loose in their slot, and the bottom could be done differently to absorb the nut so the bit will with a flusher bottom... but this works for me, for now.. Watch your fingers, cause you know.. razors.