This is a Male XT60 to Female EC3 plug adapter from ProTek R/C. This adapter will allow you to use batteries with an XT60 with a vehicle equipped with EC3 or IC3 plug; including vehicles from Losi, Arrma, Axial and more. 

Additionally, this adapter will allow you to charge your XT60 batteries on any of the IC3 equipped Smart Chargers from Spektrum.