This is the Viper R/C EZ Link Programing Card. The EZ Link is the same size as a credit card, and is used for tuning the speed control while at the track without the need for a computer. The innovative V-Port on the VTX speed control allows for programmability without removing the speed control wire from the receiver. This means less wear over time and you never have to dig into your receiver to make an adjustment. All these features are complimented by Vipers 365 day limited manufacturers warranty on all electronics for peace of mind.