Very long threaded U-bolts?

Where can I get U-bolts with threads long enough to go through a 4x4 and still have enough left over for a nut and a lock-nut both above and below the 4x4? I'm thinking 5/8". Doesn't need to be wide, 2" pipe size would be fine. Bigger is only relevant as far as cost.

They just seem more fun than eye bolts.

( Details update. )