This is the Great Planes ElectriFly Ammo 36-30-4000kV Brushless In-Runner Electric Motor. 

FEATURES

• Brushless, slotless Ammo In-Runner Motors offer an incredible power-to-weight advantage and almost twice the efficiency of Brushed motors. Ideal for direct or gear drive use.
• Up to 89% efficient and virtually maintenance-free; no brushes to wear out.
• Powered by "rare earth" Neodymium magnets for high torque and unmatched heat resistance
• Pre-installed gold plated connectors for plug and play operation when used with compatible ElectriFly Silver Series Brushless speed controls
• Double sealed bearings

INCLUDES

Great Planes ElectriFly Ammo 36-30-4000kV Brushless Electric Motor with connectors and four M3x5 machine screws

REQUIREMENTS

• Installing in model and connecting to speed control
  Propeller

SPECIFICATIONS

• Motor Diameter: 36mm
• Motor Length: 30mm
• Shaft Diameter: 5mm
• Shaft Length: 15mm
• kV Rating: 4000 rpm/V
• Weight: 138g