Electroless Nickel Class 2, AMS 2404, MIL-C-26074 is a hard, smooth, coating that can cover complex geometries with excellent uniformity. It is applied to interior and exterior of nozzle cores and is resistant to oxidation, corrosion and abrasive wear. It is a nickel-phosphorous alloy deposited by a chemical reduction reaction from hypophosphite on a catalytic substrate without the application of external current.

Electroless Nickel with medium phosphorous content (5-9%P, Type 4) is used. It has a semi-bright silver appearance. It is magnetic and exhibits good corrosion resistance. Hardness is achieved by heating cores above 500°F per the schedule given in the specification after plating causing transition from an amorphous as plated state to a crystalline structure, greatly increasing hardness.

Class 2 coatings have a minimum hardness of 800 Knoop, Rockwell c 64 or equivalent. Nominal core coating thickness is about 0.0005 inch. Standard gage cores in phosphor bronze or nickel silver are available coated with this process. To specify this coating add -01 to the coating designator in the part number.