Insert your dive boot into your fin pocket, measure the distance from the center of one strap mount pin on the side of the fin, around your boot heel
center of the pin on the other side of the fin. Select the spring strap size that is shorter than your measurement by 0.5″ to 1.5″ (1.3 to 3.8 cm).
Spring length only: Small – 7.” ; Medium – 8″ ; Large – 9.5″. Center of the buckle to buckle length: Small: 11″, Medium: 12″, Large: 13″.