Staubli Red, Male to Female Test Connector Adapter With Brass contacts and Nickel Plated - Socket Size: 4mm

Safety loop plug

Type XUG.
Loop plugs, e.g. between measuring instruments with standard, uninsulated measuring bushings and safety measuring cables.
These plugs are recommended when working with high voltages/currents, as unlike standard banana plugs, they stay on the test terminals even if the cable is pulled by accident.
With double louvres.