This is the IST F1 Traditional Rubber Scuba Diving Military Dive Fins Open Vent Fin. Traditional rubber fin with proven design. By combining features such as special blade curvature, varying degree of flexibility and structural ribs, the product is positive forward thrust with spring-like effect. The open vents efficiently channels the water flow to give added energy saving effect. Stainless steel spring fin strap compatible. (item no.: FS11) The snapback quality and many years of reliability, makes this fin an unbeatable value!