The picture has nothing to do with wagons, it's the 16' clock-tower I built for my Pennsic encampment. It somehow wandered into the wrong folder, so what the heck...
One last thing before I go to bed. I was asked why do clevis pins keep showing up?
Many of the pieces in my wagons could, indeed, be screwed together with less complexity. But I have this obsession with making my wagons able to be easily and quickly disassembled for transport. I won't be offended if you elect to make all your joints permanent. If you'd rather hoist the wagon bodily up into the pick-up bed, or if you're sure that it's never leaving home, by all means use permanent fasteners and/or glue.
I like clevis pins because they're cheap, readily available in a huge selection, and you can use things like nails and bobbypins when you inevitable lose a hitch pin.
Your Megalo-Home-Center probably has a good selection, but if you really want variety, take a drive out to farm country to the hardware store that the farmers use. You will not believe all the cool dohickies you can find in those dusty old bins. If you're not too far away from one, try to develop a good relationship with the guy that owns it. If you don't act like snotty city folk you'd be amazed at what they can help you with. I can go into the one a few miles from home, and the over-alled counter guy will nod, shift his chew, and drawl, "Whatcha lookin' fer this time?" (he thinks it's for my daughter's school science fair projects) and when I describe what weird thing I want to do he'll rummage around, and pull out the most amazing parts. When I made the tripod mount for my ballista in a heartbeat he came up with these giant sized hitch pins that go on a combine harvester that were just perfect.
Of course, if you are a farmer, you already know this.