A special link on a chain that can be opened by flexing a plate, removing a screw, or some other means besides driving out a rivet . The retaining spring clip is shaped like a fish with a round head and twin tails. This illustration helps to determine the position of the clip because the "fish" moves in the direction of chain movement. When installed in reverse, the clip may come off.
MASTER LINK
Meaning of MASTER LINK in English
English dictionary of automotive terms. Английский словарь автомобильных терминов. 2012