I was able to get the stock servo arms onto the HS-55's when I made the swap. It's a tight fit, and I almost thought better of it and used the hitec ones, but it's doable. If you have 2 or 3 HS-55's laying around, there's really no point in paying $20 for a servo from Heli-max that is, in all likelihood, of poorer quality than an HS-55 that you can pick up for just $13. My advice to anyone who hasn't had a servo problem yet, is to just swap them all out for HS-55's when you finally do have a problem.