I used 1" with a 1/2" hope drilled through the middle. You can buy it at the metal supplier like that. It makes it a lot easier to get the treads straight when you tap it. The will probably cut it the length you need when you buy it. My buddy uses it on his off-road cars and said it is more than strong enough even though it is hallow. Then if sand it with 220 and grey scotch brite it will shine them up a bit so they look better.
BammaMav727, Just a suggestion I would never run a steering bolt upside down if the nut comes off your bolt will just fall out, much safer to run the bolt the other way and also use a lock nut or drill the bolt to insert a cotter pin.