They come as a pack of four to suit different servo's, AE part number 9180
http://www.teamassociated.com/parts/details/9180/
I used to run a KO with plastic safety gear in my BJ4 at one point and it never let go, though I'd advise you get the metal replacement if you can. I use the AE1015 servo in my 44.1 at the moment with the servo saver glued up.