This is the Futaba S3151 Digital Servo.
Great for a wide variety of R/C models.

FEATURES: Digital technology gives performance advantage.
Dual Ball Bearings
Plastic gears

INCLUDES: One S3151 Digital servo with preinstalled servo horn
Four Rectangular Grommets
Four Bushings
Four Mounting Screws
One Large Round Horn
One Six Arm Horn
One Four Arm Horn

SPECS: Speed: 0.21 sec/60 degrees at 4.8V
Torque: 43.1 oz/in @ 4.8V
Dimensions: 1.59x0.79x1.42 in (40.6x20x36mm)
Weight: 1.48oz (42g)