I like 1/2" for taping the top edge of the film to the drum and 1" to tape the perimeter of the overlay. And depending on how it all goes down, you often have to put an extra layer of tape over parts of the overlay, mostly due to Kami fluid seeping out as you pull the mylar tight, even after wiping it down before the tape. You want to check to make sure that there are no little tunnels where fluid can escape. What you really don't want to have happen is for the whole thing to come undone while the drum is spinning.