The Type A roundel was most common in the very early stages of WWII, steadily being replaced as the war progressed. British aircraft of the 1930s would most likely have the Type A on all surfaces (ie. fuselage sides and both top and bottom of wings) but it was steadily phased out during WWII.

That said, mixing of different types was common; during the Battle Of Britain, most RAF aircraft used Type A roundels underneath the wings, but other types elsewhere on the aircraft.

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 sizes are 2.5mm, 3mm and 4mm.