Reefs RC Triple5 High Torque Steel Gear Digital Servo. 

Specifications:  
Waterproof: Yes  
Motor: HV Coreless 
Gears: Steel  
Bearing Type: Dual Bearing  
Weight: 2.2 oz  
Dimensions: 1.6x0.8x1.6"
Torque: 500oz @ 6.0V / 555oz @ 7.4V  
Speed: .20 @ 6.0V / .17 @ 7.4V  
Spline: 25T  
Dead Band Width: 2us

NOTE: BEC Recommended. Do not power over 7.4V