"Back in the day" the preferred servo in 1/12th scale was the Airtronics 94145 servo. So most of the kits from that time forward were and are often still designed around that servo. Hence why it comes with an Airtronics servo saver. The servo savers that use an insert are usually too big for 1/12th and have a much stronger spring than what we need for 1/12th.