This is a Traxxas Electric Motor Temperature Sensor Mount.
NOTE: In order to add telemetry to your Traxxas model, a TQi Radio System with Docking Base is required, as well as an iPhone or iPod with the Traxxas Link App installed. Most Traxxas kits require additional Traxxas chassis parts to install the telemetry system. Refer to your instruction manual, or click here for details.