If, for some odd reason, anyone with a Gotham Citizen 2 wants my torque arm file AND simultaneously finds this post,
I've been using a torque arm made of 5/8" O1 steel on both sides (decided on not hardening it, so as not to be so much harder than the axle.) There's ample leftover threadroom. The file could be *slightly* better by moving the hole down closer to the edge by a fraction of an inch. Also, you could cut a hundredth of an inch from the axle diameter, but right now it's at .393", and that's pretty decent. Plot-print and see for yourself. Works fine though. The nut whole is 6m x 1 (METRIC). My hole in the torque arm file is slightly oversized.
I use file format IPT, but these files are the converted IGS and STEP, which I believe to be wholly accurate, but yeah, be diligent and double check the file yourself.
I should add that on one side the torque arm has a triangle 2mm tall maybe 8mm long overhanging. This is because the dropout piece is slightly wider on one side, and I originally made a file for each side. I am only posting the file I actually used, which I ended up flipping for the opposite side. If your weld is exceptionally wide, then you might need to grind the edge a tiny tiny bit because I found one of the dropouts to have a slightly wider weld. The torque arm was originally made with epoxy in mind (hence, large surface area), but I added the bolt hole in the last second, because the bike already has a threaded hole there, so you may as well use it. You probably want ~13mm bolt, depending on how thick your bolt washer is. (a 6Mx1 bolt, of course.)