This is the Great Planes ElectriFly|
4mm Male Bullet to 3.5mm Female Bullet Adapter.
Connects a motor with 3.5mm Male Bullet Connectors to an Electronic
Speed Control with 4.0mm Female Bullet Connectors
Three Great Planes ElectriFly 4.0mm Male Bullet to 3.5mm Female
Connector #1: 4mm Male Bullet
Connector #2: 3.5mm Female Bullet
Weight: .08oz (2.14g) each adapter