UBB.threads PHP Forum Software Community Forums Resources and Customizing How Do I? trying to find the constraints for total board width

Control Panel -> Display Options -> General -> General Options. That's where you'll find the setting for the table width.

You can also do an opening table in your header and close it in the footer. Leave the control panel one at 100% and then you can just do all of your styling (centering) on the table in your heder.