These plane irons from a first class Japanese maker, use a high carbon steel (Blue Paper Steel #2) for the cutting edge, hardened to HRC68, laminated to a low carbon steel backing.
The result is a blade, which will take a razor edge. They will cut cleaner and last many times longer than conventional plane irons.
Fit Stanley, Footprint, Record and many other Bailey type planes.
The blade is 2.3mmm thick, If replacing a older, thinner blade a longer lever cap screw might be required.