This is the Great Planes ElectriFly 3.0mm - 5mm prop adapter with set screw and propeller nut.
Requires: Installation onto the motor or gearbox shaft
End to end length: 1.1 (28.9mm)
Complete shaft length: 0.69 (17.6mm) with 0.45 (11.3mm) threaded portion
Prop shaft diameter: 3/16 (4.76mm)
ID for motor shaft diameter: 0.12 (3mm)
Largest part of hub diameter: 0.66 (17mm) thrust washer portion
Smallest part of hub diameter: 0.43 (11mm)