This is the E-Flite EC3 Device & Battery Connector, Male/Female

Set of EC3 connectors including one Device Connector and one Battery Connector for matching up batteries to speed controls, charger leads, power meters or other similar applications.

Features:
Capable of 60 continuous amps
Ergonomically pleasing and easy to grip
Protected to avoid shorting and reverse polarity
Superior technology suited to today's advanced applications
Connectors are factory-installed with ParkZoneŽ F-27C Stryker, E-flite PNP aircraft,
Designed with convenience and reliability in mind

Overview:
E-flite's high-quality EC3 connectors and leads should be a staple for every workbench. EC3 (E-flite Connector 3.5mm) connectors, leads with connectors, and accessories are perfect for electric power applications and work with any battery, charger, ESC, Power Meter, etc.