I have Acorn windows (83). On the top of my Tube Balancer this plastic piece was used originally to hold the tube to the frame (top) and you can see it also worked as a stop. I am in need of two of these. I will be sending you photos for my balancer as well, perhaps you can help me with those parts too.
I hope you have something like this, if not I think I might be able to just screw in the tube without this piece, but I will need a stop.
Thanks for your help.
Katy