I agree with KC, I have been using the heavy duty plastic arm that is supplied with the 8711 servo for years on 8411's and 8611's (even though those two servos do not come with it).

The fit of that particular control arm and strength is superior to any other arm I have used. And I believe it is the same used by BV and his team, but not for sure.

I buy them from Horizon in a package of two for about 3 bucks, and I buy 10 packs at a time. Then again I've built 5 jets already this year using only JR servos and every one of them has been an incredible success.