High Crown vs. Low Crown
A high crown hat has a taller, more squared peak. A low crown hat has not as steep of an angle and is the most commonly used.
5-Panel vs. 6-Panel
A 5-Panel hat's front seam stops near the top of the hat. On a 6-Panel hat the front is two separate panels.
Flat Brim vs. Curved Brim
A brim (sometimes called the bill) is the stiff peak projecting in front of the cap. A flat brim is horizontally flat and a curved brim has a natural curve to it.
Snapback vs. Velcro
Both types of straps are adjustable. Snapbacks consist of two pieces of plastic that snap together where as velcro is a standard hook-and-loop fastener.
Regular vs. Small
Regular (58 cm or 22.84 in circumference), Small (54 cm or 21.26 in)