Thanks for the like, Luis.
Today's Nemrod fins are the Variador and Flipper models. "Variador" is Spanish for "Variator" and you will soon see why the fin with that name was given such a product name. Here is the model in 1974 when it was launched:
Italian: "
G - VARIADOR (Novità 74) Una vera novità nel settore delle pinne. E' possibile variare la rigidità. Placca rossa per spinte veloci, placa gialla per spinte più lente ma meno faticose. Scarpetta intera per protezione completa del piede. Taglie 44-46: 3030380; 42-43: 3030370; 40-41: 3030360; 38-39: 3030350".
Rough translation: "
G - VARIADOR (New 74) A real innovation in the fin sector. It is possible to vary the stiffness. Red insert for fast thrusts, yellow insert for slower but less tiring thrusts. Full foot pocket for complete foot protection. Sizes 44-46: 3030380; 42-43: 3030370; 40-41: 3030360; 38-39: 3030350".
1975
1976
Spanish: "
VARIADOR Verdadera revolución en la técnica de las aletas. Se puede variar el rendimiento: lengüeta roja, rígida, gran poder de palada, lengüeta amarilla, flexible, suavidad en natación, Tallas 44-46: 3030380; 42-43: 3030370; 40-41: 3030360; 38-39: 3030350".
Rough translation: "
VARIADOR A true revolution in fin technology. Performance can be varied: red insert, rigid, great stroke power, yellow insert, flexible, smooth swimming, Sizes 44-46: 3030380; 42-43: 3030370; 40-41: 3030360; 38-39: 3030350".
1977
Same caption. So a fin with variable blade rigidity to deliver whichever level of performance the user happened to require. Apart from the inserts determining the rigidity and hence the performance, the design resembles the Pro Royal down to the closed toe. Whether the insert feature is a genuine innovation or a passing gimmick will be in the eye of the beholder, I suppose.
Further Variador imagery: