Using steel M3 x 45 bolts and nuts appeared unnecessary, especially as they are expensive and hard to get in USA. 1/8" bolts in a similar length were equally elusive. I modeled these pins and they are a very tight fit in the track pieces. Once in I pushed on the "nuts" and glued them in place. Haven't tried yet as I haven't finished printing the sprockets, working out what I am doing for bearings or ordered the servos. However I have no reason to think these plastic pins won't be fit for purpose.
Downloaded from Inventor content center. Note the threads are just a graphical representation by the looks of it - when exported to STL you just get a plain pin.