The S-501 is the replacement blade for the Gyokucho Kariwaku 300 (No. 501), a 300 mm pull saw for formwork, rough carpentry and timber framing.
It has the same specs as the blade on the saw: 0.8 mm thick and nickel coated, with large teeth at a 3.0 mm pitch (8.5 TPI) and a kerf of about 1.12 mm. It cuts form plywood, OSB, general lumber, laminated wood and logs. The teeth are impulse hardened, so they stay sharp a long time but aren't meant to be filed. When the teeth dull, fit a new blade and keep your handle.
Gyokucho saws are made in Miki, Hyogo, by Razorsaw Kogyo, which was set up in 1969 when it developed the replaceable-blade saw. Gyokucho Sangyo, its sales company since 1975, sells them.