This is the Glitch Buster Capacitor from Novak Electronics.
FEATURES: High capacity super low resistance capacitor helps to solve radio
problems from high-amp motor set-ups
Plugs directly into any open channel or battery slot in any standard
receiver
Stores power from the Battery Eliminator Circuitry (BEC) and acts as
a filter to eliminate noises generated by servos
Also reduces load on BEC and improves servo response time
INCLUDES: Glitch Buster Capacitor from Novak Electronics with universal
connector
REQUIRES: Plugging into receiver
SPECS: Length: 1" (26mm)
Diameter: 0.63" (16.1mm)
Lead Length: 3" (76mm)