The World's First Fin With Four Channels Four Channels Rubberized Side Ribs Anatomical Foot Pocket ABS Buckles The Avanti Quattro has set the standard for which all fins are measured. Rubberized side ribs improve elasticity and protect the blade from cuts and abrasions The Avanti Quattro fins feature blade stabilizers to improve stability and eliminate ankle-twisting phenomena The anatomic foot pocket features interior ribs that improve fit, eliminate foot suction and prevent foot pocket flexing which transmits more power to the blade The straps feature ABS (Adjustable Binding System) SIZE:S-R-XL. Smal (36-41)- Regular (41-44)- XL (44-47) .