I want to rappel off of 10mm dynamic rope. The rope will be fed through both sides of the ATC device (parallel). Is it safe to use a 4mm cord for my French Prusik auto-block knot?
There is a similar question  but it only refers to ascending, while I am asking about descending. Note that my question covers using a Prusik around 2 parallel ropes, while with ascending the Prusik would be around a single rope (based on what I've heard from others on this thread).