If you are using a 55 gal drum, mine are 3/4 inch (four of them, but usually no more than 2 open). In my 90 gal, I went with 1 inch, but wish I had stayed with 3/4.
Pitmaker BBQ Safe
UDS Ver 1.5, 90 gallon Super UDS
Beat-up, rusted-out, still-cooking NB Bandera
Some thing that says Brinkman on it