When picking up a servo horn, it may be difficult to buy the right one for your servo because manufacturers don’t use the same number of splines for their servo output shafts. Today 23, 24, 25 splines configurations are mostly used. Nevertheless some manufacturers like Pilot and Robitronic, produce servo arms that are size wise identical but come with 23, 24 or 25 teeth configuration able to fit in all of the three above mentioned major categories.
This is the case of the Hobbico CS-170 that uses 24 splines (Hitec) instead of 25 splines traditionally found on Hobbico servos.
Below is a quick reference guide to help you select the right horn for your servos. Pay close attention to your servo because some servos are rebadged servos from other brands.