noun
clasp; metal fastener
Refers to a small metal clasp or fastener, traditionally used on Japanese clothing such as tabi socks or pouches.
足袋のこはぜを留める。
I fasten the clasp of the tabi socks.
この巾着のこはぜが壊れてしまった。
The clasp on this pouch has broken.
留め金 is a general term for a metal catch or clasp, while 小鉤 specifically refers to the small hook-like fasteners used on traditional Japanese items.
The term is composed of 小 (small) and 鉤 (hook), literally 'small hook'. The exact historical derivation is uncertain, but it has long been used for the small metal clasps on traditional Japanese garments.