Here is a big bolt that does a big job. Our 1/2-20x4.82 hex head axle bolt has a 4-1/4" unthreaded shaft to hold the rim, and a 5/8" long threaded section for the 1/2" washer and nut.
This is the strong and dependable bolt that Pride Mobility uses as the front axle on their 3-wheel Pride Celebrity X (SC4001) and Legend (SC3000) mobility scooters.