I had have used a bolt for a Fiero rear hub/bearing assembly. I used this to replace a failed assembly in a held front knuckle.
If you are using this assembly for a held setup, you will need to shave the head of the bolt to fit.
Using this in the rear you, obviously do not have any celarance problems so you can use a "non-modified" bolt.
I used a 1-inch bolt, I forget the length. I think it was around 7 or 8 inches long.
I used a lock washer with the bolt and nut and did not weld it. Welding would probably be a good idea.
You will probably have to go to a specialty nuts and bolts store to find it.
Just take a hub/bearing assembly with you to the nuts and bolts store and the match will be easy.
You also need to make sure the nut/washer/lock washer will fit inside the end of the assembly.
I also have attempted to tow a fiero, that did not have the axles installed. The wheels came off, going down the interstate.
If you are just putting the car on and off a trailer, welding the nut will probably not be necessary.
I have put about 15,000 miles, or more, on my car with just a lock washer, washer, and bolt. (rear hub on front) and have had no problems.
[This message has been edited by pdemondo (edited 07-08-2013).]