This is the Savox SH-0257MG Micro Digital Metal Gear High Speed Servo.

Features:
Over-spec refined design out performs ordinary micro size servo
The Aluminum Case design looks good and allows for lower operating temperatures
Precision metal gears forms a strong and solid framework
Strict production and quality control of plastic components
Totally Green – from materials to production, these servos are environmentally friendly
Idea for CCPM and Rudder on 450 class heli's and Park Flier Airplane's
*NOTE: Certain combinations of receiver and ESC have been found to cause "Brown Out" issues when combined with Savox servos. An external BEC, or BEC stabilizing receiver capacitor may be needed for efficient, glitch free operation in low voltage electric applications. 
Specifications:  
Speed @ 6.0V: 0.09 sec/60°
Torque @ 6.0V: 30 oz-in / 2.2 kg-cm
Weight: 14g
Bearing: Single
Type: Micro Plus    
Gear: Metal
Case: Aluminum
Output Shaft: 21T Spline 
Case Size (LxWxH): 22.8x12x25.4mm