This is the S9151 Digital High Torque Rudder F3A Servo.
This can only be used with 4.8V batteries.

This servo can produce high-current draw from your batteries.
If using NiMH or Li-Po batteries, make sure they are capable
of delivering sufficient Amps.

FEATURES: Digitally enhanced microprocessors cut about 1/2 of the response
time from transmitter input to servo reaction.
Digital operation allows this servo to reach full power immediately
and maintain torque longer.
High-capacity, high-current wire with low resistance.
Coreless motor (a wire cage rotates around the magnet).
High speed operation for immediate response.
Dual ball bearings on the output shaft.
Delivers high torque rudder operation for precision fixed-wing F3A
pattern aircraft.
Dust and water resistant (Not Waterproof)
Black plastic case.
One year warranty.

INCLUDES: One S9151 Digital High Torque Rudder F3A Servo w/Futaba J Connector
and a small round servo horn
Four Rectangular Grommets
Four Brass Bushings
Four 2 x 11mm Mounting Screws
One Large Round Horn
One Six Arm Horn
One Four Arm Horn

SPECS: Length: 1.6" (41mm)
Width: .8" (20mm)
Height: 1.5" (38mm)
Weight: 1.8 oz (50g)
Speed: 0.19 sec/60?@ 4.8V
Torque: 132 oz/in (9.5 kg/cm) @ 4.8V
Power Supply: 4.8 (Futaba does NOT recommend using 6V)

FEATURES: S9151 Digital Servo Precautions,
-It is best to avoid long leads and Y-harnesses especially with
standard grade wires. If problems are encountered, consider using
heavy duty wire such as Futaba's Heavy Duty Series or Hobbico's
Pro Series, minimizing lead lengths, and/or removing Y-harnesses.
-Current Drain: Futaba S9151 Servo is specially designed for high-
torque and high-speed, therefore very high current drain is
normal at startup. For ultimate performance when using this servo,
please review the following points.
(1) When using systems with the battery fail safe function it has
a higher cut-off voltage setting which will cause shorter
operation time.
(2) When installing the servo please check pushrod linkage to make
sure there is no binding in order to prevent excessive power
consumption and decrease the life of the motor and battery.

This digital servo cannot be used with the following * AM *
transmitters as the servo neutral signal is: 1310us).
CONQUEST AM, FG Series (T4FG, T5FGK,T6FG, T6FGK, T7FGK), New Terra-
top, T3EGX, T3PGE, T2NL, T2LGX, T2FR, T2PK series.
**** Otherwise they will work fine with current AM systems *****