The EC5 connector utilizes a standard 4.0mm bullet-type connector encased in a plastic shroud that is also polarized.  The connector is sold as pictured, you simply install the bullet connectors on the ends of your wires, and then snap them into the plastic shrouds. Take care to install your connectors as shown to insure compatibility with batteries that may come with a factory-installed EC5 connector. The  brass "male" pins must be installed into the "female" plastic portion of the connector, while the brass "female" barrells are installed into the matching male plastic piece.   The plastic portion of the connectors have the words "BATT" (battery) and "DEV" (device) molded into them, as well as the polarity markings "+" and "-".  The BATT connector is intended to be installed on the battery, using the female barrells, while the DEV half is intended for the ESC, using the matching brass male pins. Tin the inside of the brass connectors first, then insert your wires and add solder until the cavity is filled. Allow the connector to cool, then insert the wire and brass connector into the front of the plastic piece, pushing it firmly until it snaps into place. Make sure that you have the polarity correct before connecting the battery or ESC.  Sold in packs of 3 pairs.
 
Click here for additional instructions.
 
NOTE: It is the responsibility of the purchaser to ensure the correct polarity of any adapter or connector. Take note of the polarity of both the battery’s connector and any adapter you use to ensure that the red (+) and black (-) wires on the battery match the output side of the adapter. Incorrect polarity may cause damage to your battery and/or other device.