This is the Great Planes ElectriFly Ammo 28-45-2100kV 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 28-45-2100kV Brushless Electric Motor with connectors and four M3x5 machine screws

• Requirements
  Installing in model and connecting to speed control
  Propeller, suggested sizes are 10x7E-17x8E

Specifications:

• Motor Diameter: 1.1" (28mm)
• Motor Length: 45mm
• Shaft Diameter: .126" (3.2mm)
• Shaft Length: .591" (15mm)
• kV Rating: 2100 rpm/V
• Weight: 4.6oz (133g)
• Input Voltage: 7.4-14.8V
• Constant Current: 21A
• Surge Current: 40A
• Constant Watts: 310.8W
• No Load Current: 0.9A