So practical. So understated. So ...so ... bewitching. Mysterious, even. The driving cap. There are differences between the economy models, and the Heir Apparent.
An Heir Apparent will be sure that his cap is stitched to the visor, all the way across, and not snapped. Fit from the base of the skull, back at the hairline, angled a little to the front at that hairline (remember to comb your hair or smooth it down when you take the thing off, or it looks like you have bed hair). Not too wide on top, and certainly not the eight panels that the old newsboys' caps used in the 1930's. The proper driving cap has three panels. Three. No more, no less.
For techniques of sizing and measurement, see that Romania site at Romania Road Ways II, Vlad Tepes Sites.
This fetching model, on the spousal tourist-gent on Aran Island, Ireland, was lost somewhere thereafter, as I recall.
This next Irish model, at Blarney Castle, Ireland, seen from the top down, looks like one piece of fabric at the entire top, like a U going to the visor, not a lot of segments radiating out. Then other pieces angled toward the visor from the back, wide in back, narrow and pointy where they meet the visor area.
The one being held is Himself, Daniel.