My COE had hub-centered wheel attachment - the wheels centered on the axle hubs. The bolts had flat backs, no flange, and small slits in the top, like "Castellated" and "Marsden" nuts.
I do not remember if they had cotter pins (I think not).
Mine were relatively rare large Marsden nuts (image is attached, below). I found the part number, searched the Internet, and found 50 at $1 each (I needed 40).
