Reuleaux polygons are a specific shape families that have the property to have a constant width. You can roll these shapes between 2 rulers and they will stay parallel!

This is an extension of my first "Thing" on this site which was a collection of regular Reuleaux polygons. These have the same diameter of 40mm so they should work nicely as a full set with http://www.thingiverse.com/thing:61275

You can see a tutorial on how to make the non-regular shapes with inventor here: http://wp.me/p3gI7M-1E

Enjoy!