The hatinator bases seen above are worn on a headband. A hatinator is a hybrid of a hat & fascinator. Typically a hatinator "base" will have a shallow crown, hence the reason for a headband to securely keep it on your head.
Brim sizes per hat base (in inches):
Harlyn: 18.25"
UM7: 17.25"
UXXL24:
UXXL2: 19"
UXXL16: 22"
Henley: 18.25"
Jan: 20"
Oprah: 20"
Wide-side: 21.75"
UXL1: 17.75"
UXXL15: 21.75"
Harlyn: 18.25"