Sizing:
The pattern provides the instructions to make a Child, Teen or Adult sized hat, just follow the directions where rows or stitch counts are varied. They should be the following dimensions (this pattern possible runs a little large, so if you crochet loosely, perhaps use a smaller hook).
Size Circumference/Diameter at Crown/Length
CHILD 18-18.5″ 6.25-6.5″ 7-7.25″
TEEN 19.5-20″ 6.5-6.75″ 6.75-7″
ADULT 22-22.5″ 7.5-8″ 8-8.25″

Special Stitches:
The pattern uses ridging made from Front Post Treble Stitches, and Puff Stitches to mimic metal rivets. Those stitches are explained.