Although not what Tom is looking for, I thought I would mention something I have found useful for
holding thimbles for filing and sanding - a Dremel (or similar) sanding drum mandrel. These are a rubber drum with
an expansion screw in the center and usually a 1/8" shank. The drum itself comes in 1/4", 3/8", 1/2", and
3/4" sizes and only costs about $2-3 each. Worked well on my last set of pipes.
All the best
Paul