This Thing is a set of contour shapes for use in sanding. You can wrap a piece of sandpaper around the shaped edge, and use the hand grip to get the sandpaper into odd shaped places. You can also glue sandpaper to the shape - a contact cement, CA, or even a glue stick should work.
It's no mystery that this is a complete rip-off of similar sanding tools found here at Lee Valley: http://www.leevalley.com/us/wood/page.aspx?p=20183&cat=1,42500
I've offered a variety of sizes, usually in 1/8" steps, in concave and convex shapes. There are also four angled shapes, plus 13, 18, and 24mm concave shapes (which fit the common small model rocket bodies).
Note that there is no accommodation in the sizes for the thickness of the sandpaper. If you need to allow for that I suggest you scale the shapes downward slightly in your slicer.
Each shape has the size marked in text on the sides, and a hole for hanging on a pegboard or whatever.
My printer is in about a hundred pieces at the moment, so I haven't printed any of these, but it should be dead simple.
These would probably do well if printed in a flexible filament.
EDIT: I have now printed a few of these that I needed, and they worked pretty well.
This is really simple OpenSCAD, and the OpenSCAD files are included. There are variables at the top of each file that would allow you to change the length of the sander and the height of the grip handle.