Printed by my Wanhao i3 using PLA. The nozzle is 0.4mm but I made it pretend to be 0.3mm in Cura to get the spline teeth detail.
November 15, 2017 Update
Upon subjecting the servo horn to the max torque of the REV Smart Servo (13.5kg·cm), the servo horn broke at its neck due to layer delamination. So, I made the neck fatter.