Pair of Sword-Grip Ornaments (Menuki). Japanese, 18th century. Copper, copper-gold alloy (shakudō), Menuki (a); L. 2 1/8 in. (5.4 cm); Wt. 0.2 oz. (5.7 g); menuki (b); L. 2 1/8 in. (5.4 cm); Wt. 0.3 oz. (8.5 g). Gift of a Trustee of the Museum, 1917 (17.208.15a, b). Department of Arms and Armor at the Metropolitan Museum of Art
I am not sure how these are used but I have to admire the quality.
They’re used as handle ( Tsuka ) ornaments. The placement of them underneath the wrapping ( Ito ) designates the position of the blades cutting surface position upon hand index when the sword is quickly deployed from its scabbard ( Saya ).