HPI/HB servos have different numbers of splines, please see below: HPI SF-1, SF-2, SF-4, SF-5, SFL-10, SFL-10MG2: use 25-tooth servo horn HB DSJ-1SS, DSJ-1ST: use 23-tooth servo horn
Note: this is not a servo saver, it is a direct link to your servo. If your RC vehicle has a built-in servo saver these servo horns will be safe to use. Use of this servo horn without a servo saver is not recommended as you will probably damage the internal gears of your servo in a crash. Use HB #61644 if you need a servo saver.