Sorry to bud in, I've been meaning to post this for awhile. If you are bound and determined to have perfect airbrushed circles and keylines (without using decals) try using an Olfa CMP-1 circle cutter. Basically it's a glorified compass with a razor blade. It works very well for cutting beautiful circles in frisket. Just make sure to protect the point where the cutter pivots (at the center of the insert). The cutter comes with a small flat disc for this purpose. Apply very gentle pressure, you don't want to inadvertently cut the edge of the insert! These cutters are available at the higher end art stores.