This is the LRP X12L Short Course 4.5T 550 Brushless Motor from Associated.

FEATURES: 550 size, 75% longer magnet and stack for high power and torque
          Compatible with sensored and sensorless speed ESCs
          HDS (High Density Stack) technology with optimized winding for power-
            hungry short course trucks
          PreciSensor System offers precise sensor positioning for great power
            efficiency and throttle feel
          5mm output shaft
          Oversized ball bearings
          Rebuildable
          Heavy copper multilayer PCB for lowest resistance

INCLUDES: LRP X12L Short Course 4.5T 550 Brushless Motor with Instructions

REQUIRES: Motor leads, pinion gear and ESC of modeler's choice

SPECS:    Voltage Input: 4.8 - 11.1V
          RPM: 33,840
          Specific RPM/V (kV): 4,700
          Power: 850W
          Efficiency: 91%
          Magnet Material: Sintered 13.0mm
          Weight: 8.5oz (240g)
          Diameter: 1.4" (35.8mm)
          Length: 2.6" (66.0mm)
          Shaft Diameter: 0.196" (5.0mm)

                                                                   jxs 04/12/11
                                                                         ir/jxs