Thankyou for the replies. It sounds like it is a lens support.
I don't think the one I pictured in the original post is for an Arri2b or c as it doesn't have a hole for the handgrip motor.
It must be for another camera.
I would however like to buy one for an Arri2b or c, please e-mail me with a photo to:
radioencryption@hotmail.com
Thanks from,
Henry.