This is the MKS HBL850 Brushless Titanium Gear High Speed Digital Cyclic Servo. 

Specifications:

• Dead Band: 0.0008ms (Default)
• Control System: +Pulse Width Control
• Working Frequency: 1520μs / 333hz
• Operating Voltage: 6 ~ 8.4 Volts
• Operating Temperature Range: -10 to + 60 Degree C
• Operating Speed:
• @6V: 0.1 sec/60° degrees at no load
• @7.4V: 0.079 sec/60° degrees at no load
• @8.4V: 0.071 sec/60° degrees at no load
• Stall Torque:
• @6V: 252 oz-in (18.2 kg/cm)
• @7.4V: 312.46 oz-in (22.5 kg/cm)
• @8.4V: 345.79 oz-in (24.9 kg/cm)
• 360° Modifiable: NO
• Motor Type: Brushless Motor
• Potentiometer Drive: Indirect Drive
• Bearing Type: Dual Ball Bearings
• Gear Type: Metal Gears
• Connector Wire Length: 24.0 cm (9.4 in)
• Dimensions: 40x20x38.5mm
• Weight: 73g