Futaba servo horns have the numbrs 1 - 7 stamped onto them and Hitec horns have 1 - 4. If he holes in the horns are all at 90 degrees (or 45 in Futaba’s case) from each other why the need for the numbers? Or are they not exactely 90 degrees apart?
Also, do they both have the same number of splines on the output shaft? Are the horns interchangeable?
Hitec uses 24 teeth and each “click” is 15°.
Futaba uses 25 teeth and has a unique 14.4° system. 
Also the numbers are for reference in R/C use.
Thanks to the both of you for your replies. this is a steep learning curve for me. I finally built a pair of servo brackets that put the X and Y axis at the center of two servo horns so that I can make a pair of eyes look left, right, up, down, any direction I want using the SSC-32. Big step for me and but the eye movements look realistic as a pair.
