Is there another consideration? Is there a metal it is made of difference?
Ayuh,.... Ya need a piece of what, 3" pipe,..??
The size that the brackets easily bolt to with the u-bolts,...
I've seen 2, 1/2", 3", 'n 4",......
You can buy that piece of pipe from a box store, a fence place, a plumbin' place, an electrical place, a metal supply place, Wherever,...
It's still heavy wall galvanized steel pipe,.....
The plumbin' place, 'n the electrical place will sell ya 10' lengths, threaded on both ends,...
Cut the threads off if they bother ya,....
The metal supply place, 'n fence place will be bare pipe, cut to ordered length,.....
Buy a full stick of pipe from the steel supply place will probably be the cheapest way out,......
'n bein' a corner post with a gate, ya wanta go deeper, 'n bigger for more concrete, to provide ballast for the gate,.....