This is the Great Planes ElectriFly 8.0mm to 3/8-24 prop adapter with set screw and propeller nut.
Requires: Installation onto the motor or gearbox shaft
End to end length: 1.86 (47.29mm)
Complete shaft length: 1.09 (27.6mm) with 0.96 (24.4mm) threaded portion
Prop shaft diameter: 3/8 (9.5mm)
ID for motor shaft diameter: 0.31 (8mm)
Largest part of hub diameter: 1.4 (35mm) thrust washer portion
Smallest part of hub diameter: 0.62 (15.8mm)