Banana Socket 4mm Binding Post Black Red Plastic Banana Female Jack Socket Connector for Safety Protection 12 Pieces

The surface of the terminal has very poor solderability. I even used flux. Also, the heat required to solder to the terminal softens the plastic and causes the metal contact to displace for come loose.

These are hard to solder as others have said, and the heat deforms the plastic, which is quite brittle, and breaks easily. But they serve their purpose, at the end of a wire, with shrink-tube.Best way to solder these is with a real hot iron (800F) and extra flux. , get on it and off it quick.

Works great