I used to have a rolling parallel ruler many years ago and I wanted to make a simple one for nostalgia and to use to make quick and clean looking drawings. It works like a parallel bar on a drafting table. you can slide it up or down on the drawing to easily draw parallel lines. I find it works best if you move it with one finger on the center support.

I have posted it mainly as a prof of concept for anyone interested. But if you wanted to make the design the Westcott ruler was purchased at WallM*rt and I used a 3/16 wooden dowel as well as 2 rubber o rings I had laying around. They are roughly 11.5 mm in diameter. Everything goes together with a friction fit on mine and it can be disassembled.

I had grander plans but printed some small test pieces to test the fit and function. So far I am content with the result and don't see the need to print a more extensive body.

Thanks