This is a mid size servo saver from Kimbrough Products. This servo saver comes with a small tree with three different splines on it for adapting the servo saver to work with KO, Airtronics, JR, Futaba, Thunder Tiger and Hitec servos. Kimbrough makes some of the best servo horns in the business, and their servo savers are second to none! If you have a high stress application where you do not have an existing servo saver, you can use this servo saver to help save the gear of the servo during hard crashes.