Danish air force roundels; these have remained unchanged since they were adopted in 1916. I know not many people have model Danish air forces, but with Raiden's excellent Danish Fokker D.XXI they just had to be done.
These decals are scaled to represent 30", 36" and 48" roundels in 1/300 scale. (They're also ideal for large aircraft in 1/600; equivalent to 60", 72" and 96" diameter.) The actual diameters are 2.5mm, 3mm and 4mm.