2003 Corolla drive belt tensioner bold head size?

I'm going to have to replace the drive belt on my '03 Corolla soon. I understand that I have to move the belt tensioner in order to remove the old and install the new belt. What size if the bolt head that you turn to move the tensioner? I want to make sure I have the right socket before I get started. I plan on using a torque wrench to move the tensioner because it is basically a heavy duty wrench with a long handle, but if this is a bad idea I could just buy a long-handled wrench I guess...