The INK-0557 is the replacement blade for the INK 6 Siblings Plastic saw (INK-0556), the small folding pull saw for PVC and plastic.
It's the same 120 mm (4.7 in) blade the saw comes with, 0.7 mm thick in SK-85 carbon tool steel, with teeth for PVC and plastic. When the teeth dull, fit a new blade and keep your handle.
INK saws are made by Ishinoko Kogyo in Sanjo, Niigata, Japan. The company started in 1946 as Ishida Saw Works, was incorporated as Ishinoko Kogyo in 1969, and designs and makes hand saws, including its Genbaya line.