I think it's 2.5". I'll have to get it out again and measure. McMaster Carr sells the stuff in lengths of 8 ft I think but not center drilled. Easy enough to cut a little long and then face each end square and drill on a lathe. Any height lift you want, even 8 ft. Enough material to do several trucks.

Also I promise I'll post pics to assure you I live. I'll try to find one that includes my super hot wife. I'm still not sure if she exists or if someone just stole my bank account info and is stealing my money. Maybe I'm Partytruck. I'm all confused now.