茎櫃 Nakagohitsu

What is Nakago hitsu in Japanese Katana terminology?

This is a hole made for the tang (Nakago) of the sword. The tang is the part of the sword that extends into the handle (Tsuka). The Nakagohitsu is an important part of the sword's construction, as it allows the tang to be securely fastened to the handle, ensuring the stability and balance of the sword when used.