A maillon, maillon rapide or quick link is a metal link, similar to a carabiner. Maillons have a threaded sleeve which tightens over a thread, as opposed to a hinged gate like a carabiner, making them stronger, but more difficult to use. Like carabiners, maillons are available in a range of shapes and thicknesses (i.e., strengths), and often offer greater versatility over carabiners as their different shapes and lack of hinged gates allow them to be used in multi-directional load situations.
The word “maillon” comes from the French language, meaning “link”.
For maillon to reach it’s WLL mentioned in tech specs you need to use 3Nm of torque to screw the gate. For this purpose you need to use tool because it’s quite difficult to achieve 3Nm with the fingers.