The INK-0646 is the replacement blade for the INK-0645, the double-edged saw in INK's sheathed hand saw line, set up for wood and plastic.
It's the same 120 mm (4.7 in) SK-85 carbon tool steel blade the saw comes with, with teeth on both edges, for wood, plywood, laminated board, PVC and plastic. When the teeth dull, fit a new blade and keep the handle and sheath.
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.