This is the Novak Power Boost Electronic Speed Control Fan Kit.  This will allow electronic speed controls to handle more power by providing more airflow to the transistors, helping cool them better.

Features:

• Increases power handling of any electronic speed control by supplying airflow to the drive transistors
• Lightweight 5V cooling fan specifically designed for the #1865 Super Duty XR speed control, and the HV-Maxx High Voltage speed control
• Factory wired with male 2-pin JST connector that plugs in directly to the Super Duty XR or HV-Maxx speed controls
• Can also be used with the Traxxas EVX speed control or any Electronic Speed Control when additional cooling is needed

Includes:
One Novak Power Boost ESC Fan Kit with mounting bracket, screws, Y-harness to connect to speed controls that don't include a built-in connection and instructions