Wow.

Howard Banks is an expert in the field. He sent me some questions
about the appearance of the failed bolt which I couldn't answer well
for having tossed the broken bolt. Hopefully Howard will chime in
based on Andy's detailed description here. I think his suspicion was
that fatigue was a major factor which is probably supported by Andy's
description of progressive failure.

I will, at the least, change all 4 of my bolts before using my trailer
again.

GW