Carabiner
A metal clip closed by a sprung gate, used to connect rope and hardware; in rope bondage used in suspension rigging and pulley setups, ideally locking and load-rated.
A carabiner is a type of shackle, closed by a sprung gate, for quickly connecting and disconnecting components; the word comes from the German Karabinerhaken, carbine hook. Common shapes are oval, D, offset-D and pear, the pear or HMS shape being made for belaying with a Munter hitch, and gates are either non-locking or locking. Climbing carabiners carry standardized strength ratings, while keyring-style clips are not load-tested (Wikipedia). In rope bondage, carabiners appear in suspension rigging and in low-friction pulley setups, and Shibari Study advises using only ones with a stated safe working load. Shay Tiziano of Twisted Windows recommends locking carabiners rated for suspension, ideally pear-shaped or oval ones with plenty of room inside.