I was wondering if the Futaba Spline Metal Servo Horn (Tapped) FMSH-01 (Code: RB-Mxx-02) will fit the HS-755HB Giant Scale Servo Motor (Code: RB-Hit-30)
The Futaba spline can only be used with standard sized Futaba servos.
The 755HB does not have any custom metal servo horn attachments.
If you can tell us about your application we may be able to help.
The 755MG includes a selection of plastic servo horns, but we are not aware of any metal horns which fir that servo.
You can see which horns are included with the 755 here.