The 397-21 is the replacement blade for the Silky Hibiki 210, Silky's double-edged ryoba with rip teeth on one side and crosscut on the other.
It has the same specs as the blade on the saw: chrome plated against rust and pitch and taper ground so it won't bind, with a graduated rip side from 11 TPI at the heel to 7 TPI at the toe and a fine 18.6 TPI crosscut side, both impulse hardened. The kerf is 0.9 mm. When the teeth dull, fit a new blade and keep your handle.
Katsuji Miyawaki founded Silky in 1919 in Kishi, Japan, under the brand Tamakitsune, and all of its saws took the Silky name in 1983. The company is now headed by Uichi Miyawaki, and its saws are made in Ono, Japan.