The S-303 is the replacement blade for the Gyokucho Tatebiki No. 303, a 240 mm rip dozuki for tenon cheeks, dovetails and other cuts along the grain.
It has the same specs as the blade on the saw: 0.3 mm thick and nickel plated, with a metal back, rip teeth at a 1.5 mm pitch (16.9 TPI), a 0.52 mm kerf and 45 mm (1-3/4 in) of cutting depth. The teeth are impulse hardened, so they stay sharp a long time but aren't meant to be filed. When they dull, fit a new blade and keep your rattan 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.