when we purchased our 550 way back when, we also purchased the mud/rock kit to protect the front end. We moved on from the 550 to a Airstream basecamp and now a Airstream Bambi. I no longer need these and willing to give to a good home. You can keep the receiver as well. I think the ball is a 2 5/16" as we used it when we pulled the basecamp. Pick up only here in Coon Rapids, MN.