This is the Futaba S9254 Digital Coreless High Torque, High Speed Helicopter Gyro Servo with J Connector.
This servo can produce high-current draw from your batteries. If using NiMH or LiPo batteries, make sure they are capable of delivering sufficient amps.

FEATURES: Coreless motor for reduced weight and high-speed response
Digitally enhanced microprocessors cut in half the response time from transmitter input to servo reaction
Dual ball bearing gear train
Dust and water resistant-not water proof
Black plastic case

INCLUDES: One S9254 Digital Coreless High Torque High Speed Helicopter Servo
One round servo wheel, one six arm servo horn, one four arm servo horn, four grommets, four mounting screws and four rubber mounts.