Large-riveted helmet (ōboshi hoshibachi kabuto)
Kamakura period, 1185–1333
Iron, lacquer, gold, bronze, lacing
11 x 12 ½ in. (27.94 x 31.75 x 33.02 cm)
6 lb. (2.72 kg)

Dating to the Kamakura period (1185–1333), this helmet has a low, rounded bowl made of thirty-four plates held together with protruding rivets (hoshi). The warrior may have passed his hair through the opening at the top. Like many helmets of its time, this one was modified at a later date. The visor, side crests, and front crest holder were added during the fifteenth century, and at some point the helmet bowl received a thin coat of lacquer.

http://samurai.kimbellart.org/exhibit/the-evolution-of-helmets/large-riveted-helmet-%C5%8Dboshi-hoshibachi-kabuto