Looks like I’ll be going with SAE bolts for the ankle/foot hardware since larger metric bolts are as easy to find at Home Depot or Lowes. I also didn’t like the ide of threading the bolts into the styrene so am going to use a bolt all the way through with a metal sleeve to prevent the bolt threads from wearing on the styrene directly.
I’m using a 3/8″ threaded bolt, 2″ in length with a steel sleeve for the connection between the center ankle and foot. I’ve recessed the washers and glued them in place on both the bolt and the nut side to give more metal bearing on the styrene. Since the area is too tight, I cut out the left side panel to allow access to the hardware, it reattaches with rare earth magnets I bought at Amazon.
For the caster, I found a 3″ Waxman rubber caster at Lowes. Wheel diameter is 3″ and the mounting height is just under 3-1/2″. LINK
I had to make my own ‘wrench’ out of styrene since there was not enough clearance for a regular wrench.
Center Ankle hardware: $7