The screws are A4 stainless steel, the plates are a brass insert moulded into tough nylon. They are HALF the weight of the existing brass plate ones, which may not sound a lot but is a 20g saving in a quad. Add this to a set of K4 quad fins and there’s a saving of 0.2kg over a standard G10 set up – not insubstantial for the fins alone!
Strength-wise these are more than sufficient. A vice/lump hammer test showed the first failure was to shear the lugs off the back of the fin(!). Eventually with a good swing of the hammer the plate shattered destroying the brass insert along with it, but this was at a far greater load than you’d want to subject your board to even if you were hitting rocks.