Scotch "Super Strength for Heavy Packages" Cat. 3850-6.
Comes in pkg. of 6 rolls 1.88 in. x 54.6 yds. Available at Sam's Club and other fine stores. There are probably cheaper tapes out there, but they're a lot weaker.
We buy this tape for about $16 per 6-pack; about 1.6 cents per foot. A 16 x 20 frame takes about 13 cents worth. For a small shop building no more than 50 frames a week, I think the cost difference is not an issue. So I splurge a little.
The Scotch tapes are strong polyester film with a non-migrating, very aggressive acrylic adhesive. Actually not a bad outside-of-the-package tape for preservation framing. And if we place it on the outside edges of the frame, the dustcover's ATG sticks to it magnificently.
We used to buy the thinner tape Rick uses, but found that it shreds if we try to remove it. This heavier tape peels off in one piece, taking old dustcover ATG with it.
This is good, because I want to make my life easier when the frame comes back in 20 years for a mat color update. I'll be about Paul Frederick's age by then, and I might not have the patience to scrape off ATG residue.
We always fill the frame, but the tape lines pad the fitting points and make a nice, smoooooth transition from frame rabbet to filler board.
And for poly frames, the tape lines "unitize" the assembly of frame to filler board. So, a 40" square frame made of spaghetti-like poly moulding comes out solid as a rock.