The 453-40 is the replacement blade for the Silky Tsurugi 400, the straight tree saw with an ultra-narrow 400 mm (15.75 in) blade for reaching into dense growth and tight crotches.
It has the same specs as the blade on the saw: full tang and chrome plated, with impulse-hardened medium teeth at 8.5 TPI (10 teeth per 30 mm) for fresh and drier wood, and a 1.7 mm kerf. When the teeth dull, fit a new blade and keep your grip and scabbard.
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.