A plastic "clamp" for a doll holder, sized for an American Girl doll
The Makerbot Thing-O-Matic is not large enough to print the clamp all at once, so you'll need to print two halves instead. The halves are identical.
The hole is a little smaller than a 1/2" dowel, so sanding down the dowell and pushing the pieces on should result in a fairly sturdy hold. Glue is a good idea as well.
Here, the dowel is just glued to a wooden base (with a hole drilled to hold the dowel.)