Step 3: Wheel Assembly
First remove and discard the axle.
Then removed each end cap from the frame.
Connect the caps to the length of threaded bolt extending from the hub of each wheel using a washer and nut.
Just fit the caps back in to the perpendicular tube of the frame and you're rolling!
You may be asking what keeps the end caps from flying off during use. Friction alone is not good enough. What I did was have my local hardware store cut and thread a rod that extends from one wheel to the other and replaces the bolts that ran through the center of each wheel hub. When I screwed a nut to each end, the wheel hubs stay firmly in place, allowing the tires to spin freely.