All nuts are A4 316 grade stainless steel for maximum corrosion resistance.
Some examples of the places each size are used on Sharks.
M5 - Used on QR base plates
M5 Nyloc - Used on USP rudders
M6 - General rigging nut
M6 Nyloc - Used on USP centre steer system
M12 - Used on classic pins
Please contact us for advice.