Early Edo period (1615-1867)
Haruta School, 17th century
A 58-plate koboshi-bachi [helmet bowl with small standing rivets] of typical tenkokuzan form, with 30 pointed rivets on each plate decreasing in size towards the top, with the exception of the larger front plate, with three lines of rivets, for a total of 1,440 rivets.
The tenkokuzan shape of this bachi, lower in the center and slightly higher on the back, is somehow more round than usual, referring the the akoda nari line from the medieval helmets.
Although the helmet is unsigned, the shape and some other features such as the number and arrangement of rivets, suggest an attribution to the Haruta school, one of the oldest armor schools of Japan.