This design is a variation of my spring loaded clip probe adapted for banana (4mm) connectors: https://makerworld.com/fr/models/78854#profileId-83166
It uses a piece of wire (0. to 1mm diameter) a M3 8mm screw and a spring (up to 8mm diameter). A pen spring works well.
I have used a NiChrome wire here because it is impervious to corrosion and has a good stiffness but copper brass or steel wires will also work fine.
Follow the illustration in the pictures to bend and install the wire. The twisting with a drill is important as it not only straighten, but also strengthen the wire by work hardening.
I have tested this design with a variety of banana connectors and had no issue but given the diversity of existing models you should check the quality of the electrical connection for yourself.