二重鎺 Nijuu habakiDouble Collar

What is Nijuu habaki in Japanese Katana terminology?

This is a type of collar (Habaki) that consists of a bulging upper shell and a lower shell that comes into contact with the sword blade. Generally, the lower shell is filed horizontally against the sword blade, and the upper shell is filed vertically. Although it is inferior to the single collar in terms of smoothness when sheathing the sword, its high elegance has made it widely used in the treasured swords of daimyo families since the early Edo period.