The easiest 3D shape to think of with constant width would be the sphere but here are a few more. If placed on a table with a flat surface resting on top, the shapes could be rolled around with out the surface moving up and down. I was inspired to make these by Jerome Shin. As I come up with more I will add them here. these were the most simple ones I could think of. All of these should have a 'width' of 100 mm.