This is the Xpert SI-4531 Standard Size Aluminum Servo.
 Features
  - Brushless motor design provides extremely high speed, and low power consumption.
  - 4096 resolution and SIC (Single Integrated Circuit) for the highest performance and durability.
  - Aluminum middle case for optimized thermal dissipation.
  - Strong All Metal Gear
  - Glitch-free
  - Sophisticated error correction
  - High-Speed, High-precision 12-bit AD converter and CPU calculation
  - Fail safe
  - Over current protection
  - Over temperature protection
  - Start sonorant
  
  
 Specifications
  - Power Supply: 4.8~6.6V
  - Speed (sec/ 60°): 
   - @4.8V: .120 sec/60°
  - @6.0V: .100 sec/60°
  - @6.6V: .090 sec/60°
  
 - Torque (oz/in): 
   - @4.8V: 210.98 oz-in
  - @6.0V: 263.72 oz-in
  - @6.6V: 290.09 oz-in
  
 - Torque (kg/cm): 
   - @4.8V: 15.20 kg-cm
  - @6.0V: 19.00 kg-cm
  - @6.6V: 20.90 kg-cm
  
 - Dimensions: 40x37.80x20 mm
  - Weight: 62.50g
  - Frequency: 200/333 Hz
  - Range: 50~400 Hz
  - Center Position: 1520us
  - Applications: 1/10 and 1/8 Surface
  - Matching Gear replacement:  XGS72910 
  - Matching Case:  XP-01