Instead of a metal buckle, snapback caps have a press-stud strap at the back. This allows you to easily adjust the size of the baseball cap to suit your unique head shape and circumference. Typical snapbacks are trucker caps, which have both a mesh insert and press stud strap.
The majority of caps come in a one-size-fits-all finish and can be easily adjusted to suit your head size using various methods for size adjustment. This means you don’t need to know your head size. An opening at the back of the cap is characteristic of these so-called OFSA caps (“one size fits all”). This style not only provides good air ventilation but is also great for hairstyles such as ponytails, plaits or buns.
Caps with a strapback closure usually come in a one-size-fits-all finish and can be closed using a metal buckle or a hook-and-loop-closure at the back of the head. The typical strapback cap is the so-called "Dad hat", which comes with a metal buckle and traditionally has an unreinforced front.