This is RC Channel M2 Thread 4mm Ball Connector 10 pcs Gold.
For: Tamiya Buggy Champ/Sand Scorcher
The M2 thread is length 5mm
This copper ball connector is same TAMIYA 4mm #50590
Dimension is about 3.8mm of the ball
Hex screw is using 4mm tool
RC Channel M2 Thread 4mm Ball Connector (10 pcs)