●This part is used on the BEC output wire of the ESC to prevent the high frequency harmonics produced by the brushless motor from interfering with the receiver.  It is this interference that can cause "glitching"

 

●Magnetic ring (x3)
●Size:7.9x12.7x5mm
●Weight:1.8g

 

To install you will first remove the BEC connector of speed controller.  Then you will thread the BEC (3 conductor) wire through the magnetic ring and wind it 4 times as per the photo.  And last you will re-fit the BEC connector.