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core
tang (of a sword, etc.)
middle of a nest of boxes
「中心」 has another reading with different meanings.
刀の茎に銘が刻まれていた。
A signature was carved into the tang of the sword.
職人は茎の形を整えながら、丁寧に刀を仕上げた。
The craftsman carefully finished the blade while shaping the tang.
日本刀の茎には制作者の名と時代が刻まれることが多い。
The maker's name and era are often engraved on the tang of a Japanese sword.